Need advice: Mobile ATI card with 'shared' memory - EXA performance?

[Dan]

Greetings.

I'm on the verge of buying a Turion ( mobile Athlon 64 ) notebook. As 
far as I can tell, there are NO ATI cards for the Turion with dedicated 
RAM. The only cards worth talking about with dedicated RAM are nVidia 
cards. I'd prefer to use an ATI if possible.

While this will be primarily a purchase for coding work, I'd also like 
to use EXA. I've been using it on my Powerbook, and I'm quite impressed 
so far. I know that one of the big issues at the moment with EXA is 
memory consumption, and that people are recommending using a card with 
stacks of memory for EXA with lots of windows open. Where does this put 
users who have cards that share video RAM with the motherboard? Is it 
going to be horrible performance, as if I'd run out of dedicated RAM, or 
will EXA be able to use shared RAM at a respectable pace?

Dan