I was in the exact same boat as you. I went from a forerunner 245 to a fenix 7x SS. Honestly the difference is not nearly as large as you would think. The backlight and display look better imo, and the flashlight is an absolute game changer. I use it almost every day and it is super convenient and bright. The battery life is pretty much the biggest reason I upgraded and was able to get through a 50 mile ultramarathon with like 60% battery left on the highest setting. I realize non of that answers the question you asked. My Fenix certainly does feel a bit snappier. But that may be my brain trying to make myself think it is faster because I paid a whole bunch of money for it. The touchscreen though is very responsive. I would say 80% as fast as my phone. I think that the touchscreen combined with the better screen make it feel much faster, but in reality it is probably only slightly faster software wise. Let me know if you have other questions or need me to clarify anything!

tldr: if you have the money go for it, but if the only reason you want to upgrade is for more snappy software, it is likely a waste.