There's plenty of room for a large heatsink in my KT7a-raid. Striping across two ATA-100 30 gig drives ROCKS!
I've had no stability issues. Firingsquad has two very thorough reviews of both boards, with the ABIT board getting a slightly higher mark.
The good thing is, you can't lose with either board. I love both ABIT and ASUS. In my own systems, I use ABIT because I like the control and the toys (mobo utilities, soft menu, extra controllers, raid, etc). When I build systems for customers, I use ASUS, because of their stability, and outstanding support. The choice is yours, but again, you really can't lose.
Joshua