There's encouraging commentary on the the ST60 over on AV Forums, though one calibrator's opinion of course isn't consensus.
It's perhaps most important to know that the ST60 is reportedly free of the vertical bands that afflict the ST50. I can tell you that I'm looking to trade a GT50 in for either an ST60 or Samsung F8500, because of this vertical band problem.
The 55ST50 price is great, but you should try before you buy. Take along some grey slides and ask if you can watch some football before making a decision. (I'd advise similar caution with the ST60, too. It's better to be safe than sorry.)
I'd also check with the retailer that you can get a refund if you go for the ST50, as you might not spot the vertical bands until you've had time to live with the TV. At the price, you might consider this a non issue, or you might be very lucky a get a defect free ST50, though it seems only a minority don't suffer in this way.