mips

[Perttu]

What is the mips for both cards?

Meaningless information, but the 68k FAQ answers that (search for 45460 )
http://www.faqs.org/faqs/motorola/68k-chips-faq/index.html

It is obvious that the 040 at 25 Mhz willbe faster.

Not necessarily all that obvious
http://groups.google.com/group/comp.sys.amiga.hardware/browse_thread/thread/9b267d6ba27c1e7f/e767d4e5e9d625b5

http://groups.google.com/group/comp.sys.mac.hardware/browse_thread/thread/7d99d17735d0d4a6/4994fd500c37a647

What would be the most stable out of the two?

If cooling was an issue, the '030 , but assuming you have your tower adequately cooled, the '040 heating shouldn't be an a problem.

Bearing in mind the Apollo will not have the scsi fitted but the Blizzard will have.

Obviously depends on what other devices you'd plan on  adding. All IDE connectors used already ?

Or will my best bet be an Apollo 040/25?
At the moment I am running an Apollo Turbo MkIII 030/40 with 32 meg Fastram.

Since you already have a 68882 , I'd propably go with the '030. Then again, neither is that much of a jump from your 40MHz '030. 68060 would be. Depends a lot on what you do, the '040 may well be 2 to 3 times faster than the '030 in some operations.

10 to 15 years ago, if I had had the money, I would've gone with '040 in a heartbeat.