<< Since your probably swaping motherboard chipsets, I highly doubt that your win95 install will even boot. >>
As for me, I have upgraded motherboards three times on Win95 OSR2; started out with an AMD K5 133mhz friendly motherboard, upgraded to a Pentium233mmx friendly SuperMicro TX motherboard, and recently upgraded to an AMD Thunderbird 800 friendly MSI K7T Pro motherboard, all using the same install or Win95 OSR2. I've never reformatted, though I've switched from AMD to Intel then to AMD again. In fact, I also upgraded the HD once, from an 800MB drive to my present 12.7GB drive, and I just swept all the contents of the old drive onto the new drive using the utility software that came with the drive.
So this install of Win95 has been through quite a number of adventures, but it is remarkably stable and quite snappy. I don't see how people can reformat at the drop of a hat: you'd lose all your tweaks and your email and your special game settings and everything. Maybe formatting is just an easy route for people who do not want to deal with the tricky configuration issues that sometimes crop up during an upgrade. Hardware upgrades can be tricky, especially motherboard upgrades and HD upgrades. Sometimes when I'm in the middle of an upgrade and I am pulling my hair out trying to get everything working right, I say to myself that I should have just formatted for a painless upgrade, but eventually I manage to get everything working again without needing to format.
Win98 is said to have better memory management than Win95. I'm not entirely sure what that entails, maybe it's similar to the way that Intel's pentium's "speed up the internet" (ha!). Seriously, Win98 probably does have better memory management, but it really is a trade off, since anything that is gained by better management is lost in the bogged down bloatware known as IE4 (or IE5). So basically, whatever speed is gained from better memory management is lost due to the bloated IE shell. We really do need gaming benchmarks on different Windows to settle this issue definitely.
My current system gets an average of +80fps when there are 20 players on UT's CTF-Face, and in a regular UT DM map, it gets an average of over 100fps, all of this *with* 3D Audio hardware enabled in the game using my MX300 A3D sound, and a Voodoo3 3000 for graphics. It's quite a snappy gaming rig (especially for any game with the Unreal Engine) and if I installed Win98 I suspect that gaming performance would degrade.