Yeah, cobblers :-) It would have to have an 030 CPU onboard to manage that at least, and you wouldn't see a doubling in speed I don't think, anyway.
I think an 040/40FPU (plus some RAM, say 8 to 16MB would be fine) accelerator would be about right for someone not wanting to expand much further (ie. a graphics card).
YAM (my email software) is fast enough. Web browsing (with IBrowse 2.3) is slowed mainly by the AGA graphics, I don't think the CPU is holding it back in that respect, unless I were to get a better graphics card.