Originally Posted by
B1KE
I don't need fine when I'm paying money I expect a direct replacement not an older model. It's like ordering a 2015 bike and getting a 2014 model and saying fine it's still good enough. Maybe for you but not for me.
That's a little combative.
Leaving aside the length issue, you might want to take a look at how much you paid for the RD. You may well have paid less for the 4500 than you would have for the 4601. Perhaps the shop was trying to give you a deal; perhaps not but you might want to ask the shop what they were thinking.
Insofar as the length is concerned, if running a 12-30 on the rear you need the longer cage version. Is that what you have? If you do, the shifting problem is not the derailleur but the adjustment.