well it also has to be in a form of a time trial on the rally
course and an actual wheel to wheel race on the circuit. i think
Kimi should win, considering he does motoX bikes as a hobby, so he
knows rough terrain.
Petter Solberg in my opinion is less naturally talented than Kimi
to begin with, and probably not used to going flat out on a
circuit, esp if he doesn't have a co-driver next to him for the
circuit race against Kimi.
Also u need to consider what they do the circuit race in. If
they're both driving formula cars, then Kimi defo has the upper
hand because its easier to step down from a open wheeled single
seater to a tin top than from a tin top up to a open wheeled racer.
Open wheeled racers are much more demanding and tricky to drive,
and demands a lot of specialist knowledge, such as the braking
points due to the period between when downforce is lost due to
retardation in speed and sufficient mechanical grip taking over
etc.
So Kimi should definately win Solberg. Now if it were against Seb
Loeb, it might be much closer, although its very common knowledge
that drivers who started in go karts and continued in open wheel
single seater formula racers have the advantage over drivers who
came up in tin tops.