On the stock SE/30 CPU, OS 8.x is slow due to the interface tweaks Apple put into it, which really are only viewable anyway if you have a color or grayscale monitor. It was because of this sluggishness that I invested a considerable amount of my time to figure out how I could move the networking magic of OS 8 over to speedy System 7. The end result is what you read in the link I provide in my previous post, which allows your System 7.5.5 or 7.6.1 SE/30 to connect to the latest OS Macs (which is normally not possible when trying to link to OS 10.4 and higher). No matter what CPU you have, the GUI of System 7 is much faster than OS 8.x, and of course System 6 is on order of many times faster than System 7 or 8....running OS 8.1 on these systems, but I never thought people actually did it seriously, since a 16 Mhz 68030 is probably not the best CPU for running such an OS.
Even so, I still love ever more speed, so I sought out accelerators for the SE/30. I currently own two: (1) 40MHz Daystar Turbo 040 and (2) DiiMO 50MHz 030. You can read more about those cards in the text descriptions under my Flickr photos and by searching older threads here in the Compact Mac section of 68kMLA.
Nevertheless, you don't really need an accelerator to run System 7 on the stock SE/30, especially if you don't get on the web at all. RAM and a fast 7200rpm or 10,000rpm hard disk go a long way in boosting the speed of a stock CPU SE/30.