First of all, welcome to the boards! Second of all, 50 is not old, I hope to peak when I hit 50 and play my best tennis ever. I am 29 now, we will see how that goes.
I am nto sure if you have been to Tenniswarehouse.com to read the reviews on those racquets yet or not, but their specs and reviews ae always awesome!
Second, have you used any of those racquets yet? test driving a racquet is always a good idea!
The Head Liquid Metal Radical has a power level of "low"
The Wilson N5 has a power level of "medium", so does the shark
The first 2 listed had a power level of low-medium which is what I use.
I have actually not heard anything about the Prince Turbos yet. But I have always heard good reviews about the other racquets. Looks like you have a nice selection to choose from.
My thought would be to go with something at least low-medium if you have had serious shoulder surgery. If you get a racquet that has low power you will have to swing harder and who knows if that can cause more problems.
If you are an intermediate player, the NCodes can ask a lot of you from what I can tell. I have not hit with the N5, but I have hit with the NCode. I have definetly heard that it is for more advanced players. But the specs do say it is good for 4.0-5.0 players. 4.0 is above intermediate though.
I guess i need to go back to one of my first questions... Have you test drove any of them yet?