Hi mate, recently been in a similar situation for a car search, after driving a number of C63's and CLS55's, I loved them both, but found the cheaper C63's hadn't been looked after very well (may be just the ones I viewed?!) and for me the 20K ish ones were the only ones what were worth getting (condition / mileage / S/H), but you might be lucky and get a good one for less.
Only decided on the CLS55 in the end because the right one turned up, and obviously cheaper to buy / cheaper tax.
I’d definitely consider a CLS55 as I think they look amazing. There was a maroon coloured one for sale on here (I think) that was stunning.