My understanding of why a lower MTU is demonstratable better under Win95 is because the Win95 TCP stack is broken, and it is a good workaround. Most of the people raving about it are saying they are getting 2-4 times speed increases from changing their MTU from 1500 to 576. Something is very wrong there. I thought I had heard details about exactly what is broken in the Win95 TCP stack that causes this problem, but can't recall them at the moment. It could have no basis in reality and just be a rumour.
I can verify that lots of users see this as a big plus. I don't know why. There is a possibility it might have something to do with the access servers as well as the stacks. However you are correct in that the biggest win would be for MS to ensure their TCP/IP code wasn't broken in the first place. Judging by the talk at the Phoenix NANOG that might be easier said than done (though some say newer versions of DUN & Win95 fix some of the problems I couldn't verify that). Certainly changing one registry entry before shipment is a really simple fix/bodge. -- Alex Bligh GX Networks (formerly Xara Networks)