I’ve done many DVCPROHD 720 and 1080 projects using MacBook Pro with 1TB and 1.5TB G-Raids via firewire 800. Drives perform well and prices are nicely coming down during the incremental market march to eSata, and eventually a next firewire speed.
Meanwhile, also consider a 2nd firewire cardbus if you want to use two G-Raids at once for lots of resource media and scratch space at your disposal.
Performance with intense graphics is also dependent on your Mac, for one thing if you’re G5 or Intel. My MacBook Pro way outperformed my G5 dual 2.5, even though on the laptop I use G-Raids and the G5 had a full-blown level 5 fiber-channel raid.