I recently purchased a used KHS Flite 800 and is almost ready to ride minus a few maintenance items. The current crankset is a Shimano FC-5503 with a heavily worn big ring and fairly worn middle and smaller rings. Looking for replacements, I am finding lots of rings for 5700 and 6800 series 105/Ultegra cranksets. From a BCD standpoint, they are the same, would there be any other reasons that the later series rings won't be compatible with the 5500 series crank? The chain has been replaced by the PO and is still in serviceable shape, would that need to be replaced with a narrower chain for the newer rings (assuming it is compatible)?