I am a 3.5 and play up 4.0 doubles with my brother. Don't have many injuries other than my shoulder that doesn't bother me too often. I like the comfort and playability of the syn gut. Wish it were more durable and maybe offer more pop. It also moves around a lot but doent bother me much. I have been recommended rpm with syn gut or gut in the crosses or wilson nxt. I'm somewhat fit. Could always be in better shape but I do ok on that end.
Is spin a large part of your game?
Most people move towards poly, which is a stiff/slick string, for lower power (for control) and more snap-back with a full swing for more spin. The trade-off is a stiff string bed which isn't the most arm friendly. If you have mostly flat strokes, you may not get the full benefit of poly while suffering most of its downsides. Also, poly continues to stretch and then lose its good playing properties rather quickly. So though your strings don't break, it may go "dead" the same time if not sooner than you would break nylon.
Multis can provide a slicker string than s-gut for better spin. Also can have a bit more snap-back longer than sgut. And is typical comfortable. I believe mikeler has a long thread on a long list of multi strings he's tested. Generally, multis will not last as long as the sgut and are more expensive. Power can be dialed with tension.
Then there are hybrids. You can string poly in the main and cross with sgut or multi to provide much of the control and spin of the poly and the comfort of the sgut/multi. The holy grail of hybrids is natural gut/poly. The gut provides feel, power, comfort, spin. The poly helps tone down the power, helps increase spin.
You mention power. That is sometimes deceiving. Generally someone with low RHS would favor a powerful string. So without generating Nadal swing, the strings provide extra pop off the racquet. This is great for beginner players as they may have a hard time even getting the ball over the net. Intermediate-Advanced players may favor a less powerful string so they can use a full stroke to generate good RHS. The lower powered strings help keep the ball from launching off their racquets. The higher RHS can help generate more spin to keep the hard hit ball in the court.
I think you would like RPM/Sgut. Should provide a bit more spin and actual tone down your power. But it will allow you to swing a little faster by controlling the power. Gut in the crosses do not last as long as in the main. Also, the whatever you put in the mains tends to dominate the performance characteristics. Wilson NXT is a great string. It just frays like it's growing a beard in no time.