I appreciate the thorough review of both the IBM 2880W and the IBM 2000W PSU's. However, I think one more IBM PSU should be thrown into the mix once it was brought to my attention that it existed. The PSU I'm referring to is the IBM 2980W. However, it has it's plus and minus' as well. It depends on your goals and what you want to accomplish over the long haul.
CONS FOR THE IBM 2980:#1) - A "used" IBM 2980 is going for approximately $150 with free shipping. A used IBM 2880 can be purchased in a range from $50 to $85 with shipping included.
#2) - The IBM 2980 and 2880 with b/o boards will be louder than the setup with 2 x IBM 2000 BB's with b/o boards depending on the fans you have chosen and the rpm's of those fans.
#3) - You cannot "easily" increase or decrease the output voltage for some serious under clocking or over clocking like you can the 2 x IBM 2000 BB's with b/o boards and added voltage adjustment.
#4) - [For someone to add in case I forgot something]
PROS FOR THE IBM 2980:#1) - The power efficiency is better than the 2880 and the 2000 BB w/o voltage adjustment which cost extra for the 2000 BB. More on this subject provided below:
#2) - The better power efficiency saves money on monthly power bill
#3) - The better power efficiency allows for an extra S7 or A6 to be added for every 6 x 2980W's purchased. If you are using a lot of them or have plans to, the extra rig for every 6 x PSU's is more money in your pocket.
#4) - The costs difference between the 2980 and the 2880 or 2000 can be recouped rather quickly [Depending on power costs; as shown below...].
#5) - Takes up less head space than the 2000's. This may be a concern for those with lots of rigs on lots of racks going up vertically on multiple shelves.
So, for me, [with plans on 200+ rigs in the future] it is more beneficial to purchase the 2980's with b/o boards. Noise is not an issue for me. The 105 watts saved for each S7 I'm running adds up. 105 x S7's connected to all 2980 PSU's adds up to 10,500 more watts available for 8 more S7's to gain more revenue. So, I would say it depends on your plans as to the way one should go. My opinion is if you are concerned with noise, the 2000's with b/o boards is the way to go. If you are concerned with power efficiency and the ability to increase revenue because of better power efficiency, the IBM 2980 is the way to go.
Also, I have no numbers on the IBM 2000's. Yes, one could under volt the 2000's for better power efficiency. However, one is lowering their hash rate and losing revenue in the process. The 2980 enables better efficiency without losing hash rate and increasing the availability for more power for more revenue..Here is a copy of what was posted in the S7 Forum regarding power efficiency: [Please correct me if I'm wrong]The 2000w PSU is not platinum, in fact it's silver but pretty close to gold. It's younger and stronger 2500w brother is gold rated, though.
The 2880w beast is not actually platinum either, it is solidly in silver territory. I measured about 87% efficiency. Everyone confuses it with it's younger, slightly more buff 2980w brother the
39Y7414 is platinum, and much more expensive on ebay. We're all buying the 39Y
7349 which has no official efficiency numbers anywhere that I can find as it's too old to have been put through the 80+ testing program. My own testing though, puts it at about 87% efficiency at 50% load.
The 2980W 39Y
4714 shows a little over 94% efficiency at 50% load verses the 1880W 39Y
7349 at your stated 87% at 50% load.
So, let me make sure I understand this correctly;
If we had an S7 that we knew consumed 1210 watts [And used a 2980W 39Y7414 with 93% efficiency with approximately 40.6% load] we should see about 1,301 Watts at the wall on a watt meter.
AND
If we had an S7 that we knew consumed 1210 watts [And used a 2880W 39Y7349 with 86% efficiency with approximately 42.0% load] we should see about 1,407 Watts at the wall on a watt meter.
105 watts difference. It would be about the same with 2 x S7's on each PSU I believe. Let me see:
If we had 2 x S7's we knew consumed 2420 watts combined [And used a 2980W 39Y7414 with 93% efficiency with approximately 81% load] we should see about 2,602 watts at the wall on a watt meter.
AND
If we had 2 x S7's we knew consumed 2420 watts combined [And used a 2880W 39Y7349 with 86% efficiency with approximately 84% load] we should see about 2,813 watts at the wall on a watt meter.
So, my math is showing about 105 watts extra has to be burnt to power an S7 with the 2880W verses the 2980W. If we had 20 x S7's and burnt 105 watts more per S7 with the 2880W PSU, that would be 2100 more watts burnt. The price difference between each PSU is approximately $75 to $85. Let's use the $75 difference...
Converting that 2100 watts (2.1 kW) more power into dollars when using 10 x 2980's to power 20 x S7's:
730 hours in a month x 2.1 kW per hour = 1,533 kWh's in a month
1,533 kWh's x $0.10 per kWh = $153.30 saved in a month [All 10 x 2980W's paid for in 9.785 months; the price difference between 2980W & 2880W made up in 5 months]
1,533 kWh's x $0.09 per kWh = $137.97 saved in a month [All 10 x 2980W's paid for in 10.87 months; the price difference between 2980W & 2880W made up in 5.435 months]
1,533 kWh's x $0.08 per kWh = $122.64 saved in a month [All 10 x 2980W's paid for in 12.23 months; the price difference between 2980W & 2880W made up in 6.115 months]
1,533 kWh's x $0.07 per kWh = $107.31 saved in a month [All 10 x 2980W's paid for in 13.98 months; the price difference between 2980W & 2880W made up in 7 months]
1,533 kWh's x $0.06 per kWh = $ 91.98 saved in a month [All 10 x 2980W's paid for in 16.31 months; the price difference between 2980W & 2880W made up in 8.15 months]
1,533 kWh's x $0.05 per kWh = $ 76.65 saved in a month [All 10 x 2980W's paid for in 19.57 months; the price difference between 2980W & 2880W made up in 9.785 months]
1,533 kWh's x $0.04 per kWh = $ 61.32 saved in a month [All 10 x 2980W's paid for in 24.46 months; the price difference between 2980W & 2880W made up in 12.23 months]
1,533 kWh's x $0.03 per kWh = $ 45.99 saved in a month [All 10 x 2980W's paid for in 32.62 months; the price difference between 2980W & 2880W made up in 16.31 months]
LETS NOT FORGET THE EXTRA 2,100 WATTS AVAILABLE IN THIS SCENARIO ALLOWS FOR AN ADDITIONAL S7 FOR MORE REVENUE WITH ROOM TO SPARE. 
