Hands down...Antec 300
I have the Antec 300 and Coolermaster 310 elite. The CM is a nice case but airflow sucks. I have to leave the side panel off otherwise it gets too hot.
Antec 300 I have all the fans running at minumum speed and it cools just about as well as if the system was on the bench.
Just for the record:
CM 310 has x58/ UD3R, 920@ 4ghz 1.25v, gtx
260@1550 shaders; running WCG and gpugrid. 100% load. 920 is cooled by megahalem so I cannot add any of the fans for the side panel.
If I run the front fan, it actually make the system run hotter for some reason. So I basically have the CPU fan, and exhaust fan along with having to keep the panel off.
Antec 300: Biostar Tpower
920@4ghz@1.25v cooled with TRUE.
2 GTX
275's@1620 shaders.
This system runs WCG and
F@H 100% load
I run the 2 front fans, top fan, exhaust, cpu fans, side panel fan.
Its really quiet and cools really well. I am very pleased.
The CM may be ok for your needs, but for me I will have to mod it to make it work for my needs