When used in an SE/30, the only difference between a IIfx and IIsi rom simm is that when you use the IIsi rom, it will boot up right away as normal when you power on the se/30. When you use the IIfx rom simm, when you do a cold boot, you will get garbage on the screen for about 25 seconds (give or take), and then it chimes and boots as normal.
Most people want the IIfx rom because it is a lot easier to find and a lot cheaper. The IIsi rom simm is very hard to find because only very few IIsi's had a removeable rom simm. The vast majority had the rom soldered to the logic board.
If we still had access to the old forum, the thread JDW made about 1.4mb floppys not working with his 040 and IIfx rom simm would explain a lot, but sadly, it and many other goldmine threads were lost forever.
Most people want the IIfx rom because it is a lot easier to find and a lot cheaper. The IIsi rom simm is very hard to find because only very few IIsi's had a removeable rom simm. The vast majority had the rom soldered to the logic board.
If we still had access to the old forum, the thread JDW made about 1.4mb floppys not working with his 040 and IIfx rom simm would explain a lot, but sadly, it and many other goldmine threads were lost forever.