if its ide , then a powerflyer is one option , but you dont need a powerflyer to use big hdd's , i use big hdd's (+160gb) and i have no probs with them on eide 99 , idefix 4way adapter , powerflyer)
partsions are as high as 75gb , dont need em to be bigger, anyway you should use SFS or PFS 1,2,3 on the big hdd + system "MUST" be on the first sectors on your hdd (not bigger than 4gb).
cool that u found all them gizmos! ..
good luck!
pps: afaik u can hook up that hd with no problem even on the normal pio0 controller thats in your a1200. (but i am not 100% sure...)
and for speed... yes an powerflyer is the only REAL option then , or get an scsi2ide adapter so yo can hook up an ide drive to your scsi chain (if u have that)