what model number is the Gen 4 Ohlins TTX?
KA364 for Gen 5 I see you wrote....
KA364 according to www.ohlins.EU
If it turns out that KA364 uses from factory a spring 95...105, then it is a hint that gen5 link ratio is similar to aftermarket link. In this case I would wait selling your Ohlins (gen4) shock, if it is valved for aftermarket link and you weigth, then just install it on gen5.
If gen5 shock is longer, then just add clevis shim to balance. If it is shorter and gen4 Ohlins will be too long, then Ohlins must be opened and made shorter by adding washers below topout spiring.