The 7700XT is much faster in compute but that’s perhaps not as important as it having somewhat greater memory bandwidth (430 vs 380GB/s). That is going to help.
And as you say there’s also the Wave Matrix Multiply Accumulate (WMMA) support which may give a nice boost too.
The RDNA3 part would seem to be the way to go unless pricing is very different.
There’s not much in the way of comparative ML benchmarks out there so hard to say really. There is this test which shows the 7700XT being 300-426% faster than the 6700XT in Stable Diffusion (depending on image size) which is a significant difference.