I have a rig with 3 Sapphire 7950s in it; two are the exact one that you linked: 100352-3L and one is a 100352-2L. I would say that the 3Ls you linked are good cards for the price. That said, I feel that the 2L I have gives me a good frame of reference for comparing the 3L card to others. All around, the 3Ls seem to be a cheaper-made card than the 2L but this is not necessarily a bad thing; they still work well. Compared to the 2L, you cannot adjust the memory voltage on the 3L and there are no VRM temperature sensors. The heatsink on the 3L cards does not seem to be as good (less copper) and so for any given temperature, the fans on the 3L cards run a little bit higher than those on the 2L. Cooling of the VRM components looks to be fine as they have a decent-sized aluminum heatsinks attached to them.
I get exactly the same hash rate for my 2L and 3L cards at any given setting. Their overclock/undervolt capability is nearly identical. If I recall correctly, ~1070Mhz core/ 1250Mhz memory will take them to ~625Kh/s at ~1.1V. I've pushed them above 630Kh/s but I don't mine that high as it kills efficiency. Due to power costs, I tuned my rig for maximum efficiency. Here are my current scrypt mining results:
3x Sapphire 7950 100352-2L/3L
562Kh/s per card, ~1.68Mh/s total
Windows 7 x64, Catalyst 12.8 (I tried many drivers, 12.8 seems to provide me the best results for 7950 cards)
Cgminer settings: --intensity 19 --thread-concurrency 24000 --worksize 256 -g 1 --lookup-gap 2
Core clock: 944Mhz
Memory clock: 900Mhz
Core voltage: 980mV actual (1037mV set in TriXX for 3L, 1018mV for 2L)
Core temperature: ~62-65C, 40-48% fan speed
VRM temperature: ~70-73C (as reported by the 2L, no sensors on 3L)
Room temperature: ~65-70F (~18-21C, air-conditioned)
Configuration: Milk crate rig, 20inch box fan on low setting blowing through the crate.
Total system power usage: 620W at the wall - powered by an 850W silver-rated PSU (XFX PRO850WXXX)
The system uses ~55W without any of the cards plugged in so each card uses only ~188W while mining after PSU efficiency losses. This results in about 2.72Kh/s/W compared to 2.35Kh/s/W when running the cards at 605Kh/s each or ~2.1Kh/s/W when running them at 630Kh/s+ each.
To answer your questions directly, if the cards work as well for you as they do for me I think that you will have no issues with heat, especially if you don't mind undervolting. If you run the cards in a very warm environment, or without airflow, you will definitely need to undervolt them a bit. As to the fan noise, they're quite silent under 50%. Up to about 60% they're not very noticeable. Around 70%, you can tell they're running for sure. At 80%+ they really start to pickup and can get quite loud.
When I first got these cards I had trouble getting them to change their voltage. I tried all kinds of software and did different things to get it to work. I don't remember exactly what did it but here are two things that I remember: On the top of the card is a button to switch BIOSes. I'm running the cards with the second BIOS (the button is depressed and glows blue). I also updated to Sapphire TriXX V4.6.0 and that's what I can finally use to get the core voltages adjusted. I'm not sure if the BIOS button helped or if I just needed the newest TriXX but I figured this might save you some trouble if you have the same issue.
For reference, the cards:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202026 <---100352-3L
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202006 <---100352-2L
I know you didn't necessarily ask for a comparison but I thought this might be helpful to give a point of reference and maybe for someone else who already has some 2L cards and is looking to pickup some of these 3Ls too. Hopefully this helps you out.
