the cassaroll does EVERYTHING... but to do it you'll spend twice what you want to spend now.

i got the schwinn world street pictured below(without panniers but WITH disc brakes, fenders, and a rack) for 500. it's got gears and it's not very hip looking, but damn is it a good bike for getting around no matter what. 32c tires are fast enough and so much nicer to roll on than the kilo with its 23c's.

if i didn't live in a hilly city i'd love to just have one, awesome bike... like a cross bike or a track bike... but my taste is a little more expensive than yours. and at 6'4" you're going to have to play around with stems and seatposts on anything but a custom frame if you really want comfort and longevity. the bigger your body is the more a slight difference in fit matters.

basically, if you want just one bike under 500 and you want a singlespeed, you're not going to do better than a 9-2-5 or similarly equipped bike in your size. for that price, it really doesn't get any better.

if you were willing to spend more, it would depend. if i was never going to add gears and i never ever needed to add fenders or anything, i think a Felt Breed would be about as good as it gets while keeping the price down. a salsa cassaroll is excellent but by the time you build it up with the parts it deserves, you've dropped a grand.