I had an X600SE 128MB and it worked well on the game maxed out.
My old system:
Pentium 4 3.00 GHz
128MB X600SE
2GB DDR400
I had to have an X600SE because I needed something low-profile. I had a tiny Dell at that time, so an X600SE was one of my only real choices. Eventually the X600SE exploded.

I then replaced it with a 6200TC 256MB and it worked fine on the same settings. An X600SE 128MB can (as far as I can tell) run things a little better than a 6200TC in terms of performance.
My new computer plays the game even better (new computer was originally for Battlefield 2, so it's overkill for SH3):
Athlon 64 X2 4800+
256MB 7800GT
2GB DDR400