Since this is the thread linked to from the FAQ for Optifine, I'd like to mention that it /is/ possible to get Optifine to work with the 1.6.4 packs. See this thread for more details (read the WHOLE thread!):
http://forum.feed-the-beast.com/threads/direwolf20-1-6-4-optifine-wont-work.35468/
http://forum.feed-the-beast.com/threads/direwolf20-1-6-4-optifine-wont-work.35468/