it really depends as stated at www.2cpu.com(upaboveit wrote the scsi raid faq there and gave this answer to me when i was looking into scsi raid on my rig i have yet to add this to my rig as i'm still saving lol) 2 scsi hdd's in raid zero wont max out a regular mobo bus and 4 would only max out the bus when at max str's ie if you are transfering huge files all day long then yes obvously you want a bigger bus (server board) but if all your transfering are small (less than 1 gig files or ocassional large files)then you should be fine
if you are looking at two drives raided a 32 32 bus should be fine
4 drives raided you might look into 64 32 buses
and anything over definately go for 64 64 buses
now before you go shooting me and all i'd still recommend if your going to spend the money on scsi raid get more headroom than you need especially if you are considering adding on to it later but on a gaming rig ?then a standard bus should be fine