So you can still fly VFR on top with an IMC rating. How do you know if it's VFR on top though?
You mean how do you forecast cloud tops?
With difficulty. I have some info on the subject
1 2 but they are really applicable only to higher altitude capabilities which is meaningful only with an IR. The IR images
e.g can indicate cloud tops.
In the IMCR context, you can fly around the N of England fairly well, ~ FL060, above cloud. In fact the other week I flew from N Wales all the way to the S coast, FL055, above solid cloud. It can be useful.
More practically, if you look up at the sky, the base is say 1500ft and you can see blue sky in holes, the tops will probably be 3000-5000ft max. And if they are higher, you can just stay in the stuff, or descend back down below, etc.
I like flying above cloud because it is usually very smooth, whereas flying below can be very rough (esp. in the summer).
Your radio nav has to be spot on.
VMC on top works much better abroad because over there they don't have the low level Class A, and ATC more readily allows CAS transits there (Italy excepted; lots of Class A).