Shimano Hollowtech 2 road BBs, whether pressfit or threaded, accept any shimano hollowtech 2 road crankset. Swapping cranks is a breeze, you don't need any new bearings. Make sure to read the manual on proper installation/removal. And check your shifting afterward- you may not need to make any adjustments at all, but I couldn't swear to it.

You won't save any weight moving to the 6700 (aside from $200 from your wallet ), but I'm a fan of the shifting on those hollow chainrings (it's not something you'd notice in a blind test, but the difference is there), and the 6700 crank is much more aesthetically pleasing than the current one. Once you've done the crank swap, the only other upgrade I'd ever possibly bother making on that bike is the wheels, and that's only if you love the fit and feel of the bike, you have $600+ burning a hole in your pocket, and you want to shave a pound off the bike.