You're right, it's only up to find out how to drive fast in this particular piece of software... Like in all sims.
@ waters: i was watching the top split race
at Laguna Seca earlier this day, with an alien doing his 1:37s in front but P2 to P4 did average laps of 1:40-1.41, and the drivers on P5-9 had 1:41-1:43.
(btw: the winner of split#2 did 1:41.7 average)
So, if you can do 1:40 laps average, it's more than enough for the beginning - that seems to be good for a mid-field position in top splits or maybe top 5 or 3 in lower splits. All you have to do is not to spin and do a good average pace.
I've started testing on Suzuka (with the recommended settings of the tuning guide, +2SPO/5ARB/20PSi/58%BB) and was able to do a personal best of 2:27.1 with optimal lap of 2:26.2 - and that just after two hours of testing.
The optimal lap will be enough to reach the top25 lap times.
(didn't test it on Laguna Seca yet)
It can't be a big mistake to give it a go, and to only do some minor changes later to find your best balance.
Edit: tested same setup on Laguna Seca - works fine, i could set some new sector bests, not much but a slight improvement - all in all it's nicely driveable for me