I had the previous gen. and now the new tower model and use(d) both for TM backup over GB ethernet. They are both slow as hell in that TM star field interface you mentioned. Like you said, click up a couple days to go back and just sit there and wait several seconds while it scrolls to where you want.
I like the AC wireless improvement, but if you are thinking of buying the new gen. for improvement in this specific area... don't bother.