I was thinking it might be good to turn down the memory clock, but I wasn't sure if I'd lose stability due to the memory falling behind pace with the core. Also, I will consider the bench.
Not to worry. I don't even know if the memory on the GPU's is being touched while hashing SHA256. You can safely down-clock your video memory to 300 and have them happily mining away at much cooler temperatures.
Now if you are hashing Litecoin/Scrypt, that's another matter entirely, and you'll need to keep your memory normally clocked AFAIK.