Purely anecdotal here, but as someone who played Project X Rifle 6.0 for a decade and switched to PX LZ 6.0 in my T150s (fit in 2023), I'm not sure you'll see too much of a difference between the two shafts. I know PX LZ are supposed to load better and have a bit more flex, but I couldn't tell much of a difference in feel, contact, and measurable stats when hitting them side by side. The only reason I switched to PX LZ's at the time is because they were generating a little less spin for me on the trackman. Distances were almost identical and peak height was slightly higher on the PX LZ.
If it were me, I'd save the money and headache for the swap and start playing the PX 6.0 Rifles.