VHF/UHF

I'm exploring WSPR for the first time. This is also my first attempt at a digital mode besides morse code. I'm not clear what the maximum spottable frequency is.
I'm using my old Dell lap-top running Win98SE with an FT-817.
I intend to try 6m, 4m & 2m with WSPR. I would like to try 70cm & 23cm.