Yeah...I'm w/sstorkel. Ride it for awhile first and see how it does for you on your regular routes. Any changes you make to it are going to be made after it's already assembled, so it won't save you anything having it done now. Plus, none of us can really answer your question. As lambo said, only you...

I also am about 260#. I ride a 53/39. I have 3-cassettes: 11-23, 12-25, and a 12-27. Riding in SoCal, I encounter a wide array of hills: rollers, long-long mountain passes, short mountain passes, short & extremely steep hills, long steep climbs. My 12-25 has served me well on many of them. I got the 11-23 for flat races. I got the 12-27 for the King of the Mountain series and the Assault on Mt. Mitchell last year--all extremely challenging rides (100-miles/10,000ft+ each). It really gave me a last bailout gear for when I was tired. I used it alot during those rides.

I get almost all my stuff at probikekit.com. Cassettes run around $60--$90 there, (usually) much cheaper than an LBS. Check 'em out.