From my own experience, my A2000 had 16MB 32-bit fast on my GeForce 040, and there was a definite performance improvement when I added 8MB 16-bit fast (via a SupraRam card). Even with 3.9, BB1-4, and various other hacks & speedup patches, there are still some programs that look for 16-bit memory first. It was definitely worth it to me to add some. Your mileage may vary. 
Interesting. I wasn't expecting that, I've heard a few times that mixing 16 and 32 bit memory slows the accelerator (not necessarily the transfer performance of the SCSI interface).
Your GE-Force has a SCSI interface included, right? So your 2000 doesn't have an A2091?
I asked because I have an A2500 with Commodore's 030 accelerator, 32-bit fast ram, A2091, and NO 16-bit Fast Ram anywhere (the Chip Ram is 16-bit, of course). It makes sense to me that some ram on the A2091 would improve its transfer rate, buffering, etc.