Yeah, unfortunately sprinting seems to be server-side in 1.6 now due to the way the new Entity Properties system works
As for the FPS drops, are you on a laptop or other machine with dual graphics cards (one for power saving, one for gaming)? If so, your machine is probably using the power-saving card, due to a bug in Mojang's 1.6 launcher. Look somewhere for an option to disable automated switching and always use the dedicated card.
English: our servers are technically still 1.5.2, but they are only able to be connected to by 1.6.1 clients. You can't get genuine 1.6.1 CraftBukkit until they update for 1.6.1, and once they do, we'll follow suit within a few hours.