Thought I'd post my results on underclocking memory.
I run an ASUS 4870 DK using poclbm -w 256 -f 60.
Trying the clocking around I got to ~92.5 MH/s @ 830 core and 900-300 memory using MSI Afterburner.
After trying to go lower I started to see a hash boost when going below 250. Going lower, I found that @ 173 and lower my card immediately froze, and less than 185 it would crash and do a VPU reset after a small time.
But at 190 is a sweet spot for me. Hashing increased by 2-3 MH/s compared to anything above 250, and as a bonus the card runs a lot cooler, practically flatlining at 61 degrees at the moment.
It is also pretty effective, pulling that by only using 85w over when sitting idle, or about 1.1 MH/J.
http://imageshack.us/photo/my-images/196/unled1yxj.jpg/I'm a happy new miner.
Edit: Pumping core up to 840, my card sits pretty stable at 95.7 MH/s and 62 degrees. Using -w 256 -f 10 makes me go up to 98.4, though windows becomes sluggish then.
I can run at 850 core and get 100 MH/s, but at that point if I so much as touches anything that causes extra GUI operations, the drivers crash.
Before when I clocked core to 850 with standard memory clocks, the card would crash instantly, even when not running the miner. So underclocking memory is a great success I'd say.