Uhm, so yeah... before I consider "upgrading" to SP2... how can I be sure this won't affect my BitTorrent and gaming experience? And if so, how to disable it?
It won't. I am using XP SP2 since the beginning and basically a few weeks later all P2P apps adjusted to the new behavior.
Note that SP2 does not limit total number of connections in any way (as is wrongly reported on many places) just number of half-open connections per sec. That will only affect those P2P apps that are frantically trying to connect to as many peers as possible... Like I said, all high-profile P2P apps are already patched and are not susceptible to this limitation.
I would recommend not to install any kind of patches, there is no need for that. You'll just risk that next SP does not update the patched file...