And am I wrong in thinking that by going to the 13.5" from the 13", it wont really be noticeable? From a 12" to a 13.5" I would think may be noticeable, but I am guessing I wont visually even notice that extra 1/2".??
If you get a same length shock that has a longer stroke v/s the exact same stroke, only the rake and trail is effected which on these bikes is minimal. If you raise up the frame and get more air under it the lean angle can increase. If you take a 13" OEM air shock with 3" of stroke and minimal sag (1/8"~1/16") and which means no rebound, including a very inferior design and parts, FrankieB is correct. Not much difference on a 1/2".
The OP stated that he was going to change technologies, than the performance upgrade would be which shock technology was used, which tuner built it, and how well the end user knows how to adjust the valving & spring pre-load/sag.
This is your OEM air shock, notice that this is a twin tube design and there is no air valving. The air only sets the spring pre-load on both shocks. Look to see how it works.
The same shock but I put a 46mm Penske piston (aqua arrow) under the 20mm OEM air shock piston. The piston is what controls the swingarm/wheel from the frame.
A shock that is not gas charged produces air bubbles when the shock internals move. This can be seen when rowing a boat where you squeeze the air out of the water when rowing. Cavitation makes the shock not work properly.
The whole idea is making a shock support the bike & movement than making the spring value to just equal gravitational pull, lets the wheel go over the road irregularities while the frame stays stationary. You can not make a shock/wheel adhere to the road if there is so much stiction that the frame must move which slows down the shock action and lets the wheel float. When the frame is moving the ride is rough and the rider is unhappy.
In this race bike a small camera is attached and watch the swingarm/wheel move but the treeline and frame does not.
Bottom line is to just to increase the length of the shock will have little benefit but to install a superior shock would increase riders satisfaction and comfort depending on how the shock was built.