Thank you for the replies, but I do know the difference between a freewheel and a cassette. Funny how nobody actually answered the question. The question pertains to the difference between the HG50 and HG70 lines and if the 12-28 7 is a good replacement for the 13-26 6

The current group is Exage Sport 6 sp SIS. Hub is cassette. Yes, building new wheels out of 105SC hubs. Yes I know I wiill need new shifters and derailleurs, bla bla bla. Now, can some one offer an answer tot he original question? Thanks