Just reading some comments on this thread regarding the C63 and as someone who owned an IS-F and moved on to 6.2 C63 I have posted my initial impressions on the IS-F forum already a few months ago.
I was not and am not a big Mercedes fan - I'd still have my IS-F if it weren't for practicality reasons but I've found the C63 slightly quicker than the IS-F. With a remap it will certainly be quicker than the GS-F and RC-F too. I agree though that +-0.1 or 0.2 seconds to 60 does not make or break a car.
I would say that the Lexus is better built and feels better built too but I bought both cars with a main dealer warranty for peace of mind. Probably not necessary on the Lexus though!
My C63 on 18" wheels rides better than my early IS-F. I didn't drive the RC-F as it didn't fit my needs but would certainly consider a GS-F in the future.
The 6.2 AMG engine feels a little (but noticeably enough) quicker and as @Stuno1 has stated is easily remapped to 500-515bhp as the engine is detuned in the C63 to avoid upstaging the E63, CLS63 and S63 etc when they all used the M156 engine.
Regarding the C63 having a greater proportion of 'yob' owners - I went for a debadged silver estate on 18" wheels in a bid to avoid unwanted attention.
Talking of attention though, the exhaust imho is one of the best standard exhausts on any normal five seater car. It's quiet with a nice burble when pottering along but nice and loud with pops and bangs when pressing on.
I know the comparison being made here is RC-F v C63 and I'm not addressing this specifically but with the choice of NA V8s reducing all the time the Merc 6.2 engined cars will probably hold value relatively well due to the following AMG engined cars have. As good as Lexus V8s are, they just aren't as widely recognised except by true enthusiasts resulting in limited new and used demand. Good for us when buying a used F though!
Each to their own though, the IS-F, RC-F, GS-F and AMG V8 engined Mercs are all very good cars 😀