Trek 5200 crank question
 

Ultegra 6500 Double 53/39

There is no option for the 6500 in 50/34 that I can find. I need the compact for sure. My knees don't like the 53/39. I do have an 11/28 on the back though. Suggestions? I don't mind moving down to a 105 crank in 50/34 if I had to.

Thanks in advance

At the time of 6500/5500, Shimano did not make a compact crankset in that series.
You can go newer 10/11 speed, which will work just fine with your other components, or older MTB cranksets, which can accept compact rings, or something like an FSA compact crank with a square taper BB.
Whichever way you decide, a new BB will also be required.

That Trek model was also spec'd with a triple. You may want to look into that.

FWIW: I had a '00 5200 with a 52-42-30 triple crank. Made no sense to have a triple in pancake flat Sacramento, so I changed it to a DA 7800, which was the first Hollowtech II crank/BB. Lighter, stiffer, a game-changer.

Anyway, a newer compact 105 crankset will be an upgrade over a Ultegra 6500 for sure.

I would agree if your struggling with the 53/39 a triple may work better for you than a compact. Most 8 or 9 speed Shimano triples should work with a matching BB you will also want to get a new chain.