I have had an ASR5c since Jan this year. In answer to your questions.
5’9″ medium
70mm with a 685mm low rise bar
In line post
None
Not for a second no. Combination of the geometry, lowish bb, stiff frame and light weight are a perfect combination IMO. I have been surprised at how capable it is. I have an 07 575 which I intended to use for harder hitting stuff, but I have not felt the need yet. Not ridden anything particularly big, but I have never felt underbiked riding in the Peaks. Incidentally, I’m running a 120 mm SID fork and there is scope to increase its ability on more challenging terrain by fitting a 130mm or 140mm fork. I have a 150mm Rev that I been meaning to space down to 130mm to try it out, but haven’t got round to it yet.