The update from id Software and Raven is designed to improve performance on systems with HT Technology, multiple processors, or dual core processors. According to the text document released with the update, users can expect performance gains "of anywhere from 25% - 87% depending on processor type." These are impressive claims and early reports do seem positive in regards to performance. However, some users have been reporting problems with Punkbuster, with many getting kicked from servers.
It might be worth waiting for a final update to be released as this version is still in the beta stage, but if you must have the best performance then you can get the Retail v1.0.5 beta patch for Win32 over at 3D Gamers.