@rvo_nl
I've had quite the opposite experience. Many demos were made to work on a blizzard 1230IV, simply because it was one of the most popular accelerators around. 040's were a bit more rare in the demoscene, while 060 were a bit more common.
I guess you mean '90 demos because most >2000 demos were designed for 040/060. In fact the c2p designed for 040+ will perform badly on 030 and if your software needs fpu you'll raise the cost of the 030 so much that you'll be able to buy a 040/40 for almost the same price. For 030 demos it's a good idea to run cyberpatcher/oxypatcher to improve compatibility a little.
@koshman
I'm not sure what you're talking about, but I'm talking about the RAM that's on the turboboard itself. Of course, I have the usual 16MB A4000 mobo RAM, but with A3640 it still feels subjectively slower than 1230 MKIV. I don't have any benchies, I simply remember quite a few demos that were slow, but still enjoyable on 030/50 that are nothing more than a slideshow on A3640. I'm not saying the A3640 is slower across the board - it might well be faster in WB and serious apps, but that's more difficult to judge.
Demos running faster on BlizzardIV 030 than on A3640 is definitely not normal. In the worst case they'll run the same but 040 is usually smoother even running at 25Mhz. Enable MAPROM if you don't have it enabled and relocate your kickstart to fastram. Even if your 040 has fpu it doesn't mean using fpu versions will always be faster. Do you have the caches enabled? Are your simms ok? Do you have 68040.library correctly installed? Check your motherboard jumpers.
If you fit a gfx card you'll notice even more how slow 030s really are compared to 040 (even A3640/25).
In the worst case and if you dare you can try to overclock your board to 28Mhz (30Mhz too, I think 33Mhz may require small changes) and the system may feel slightly smoother.
Anyway, on an A1200 a 040 beats a 030 easily and allows you to run 3D games and demos much better.
@Thorham
I try to stay away from 030 as IMHO they feel slow (much more than half the speed). Using CED obviously doesn't need much cpu power but if you built moderately large programs you would notice the benefit of a 040 or 060. 030s and 040s are is quite different from a programming point of view (faster FPU available in 99% of situations, bigger caches, longer pipeline that allows more instructions per cycle...). Of course you could argue that since you are coding in ASM a 030 is enough but you could argue the same about a 020 :-) And you could argue that you like coding entire modular OSes is fine with a 68000... but WB programs would still feel slow on it. Try IBrowse with some page with images and you'll notice the difference.