I don't think I'll ever trust IE. Microsoft keep making it harder on p2p users. They hide updates within updates to mess with my half-open connections and my TCPIP settings. Microsoft doesn't let the consumer think for themselves and force changes we may not want. I'll stick with Firefox. Before that it was Netscape.
Like I said I also like Firefox, but I really don't think that IE has anything to do with your half-open connections. If I remember this correctly they lowered the number of connections to stop virus infected computers to spread the viruses to other computers too quickly. From what I remember the number of connections were possible to change in NT and maybe Windows 2000/ early XP. My bet is that you have run the hack for this(EvID4226Patch.exe), because I remember running this myself after seeing a bunch of error messages in my event log. Every now and then there will come along an update that will replace the file that this hack "fixes". Wether you use IE or not won't matter. Maybe you can avoid this by uninstalling IE alltogether, but my guess is that you won't because I think these are fixes to XP. Anyway you can just run the hack again after you run an update and you are back in business.
I know you are right about p2p running slower on fast connections because of the limit, but I don't really think Microsoft was targeting file sharing programs. It was just a result of them fixing other problems.
The point I was making however was that it is good practice to run Microsoft updates if you run XP. I am no expert on this, but the guy resposible for security at the place I work keeps stressing how important this has become lately. The reason is that every time Microsoft discovers a security issue they start making a fix. When they release the fix this becomes publicly known. People who want to exploit the security issues will use the fixes as documentation of how to exploit the operating system and within a few days someone has been able to do this.
Okay, a long post based on lacking knowledge, so feel free to correct me, but please don't flame.
Regards
Popol Vuh