In my experience with a big bore (KDX200 to KDX240), I did go leaner on the jets. But the engine consumed more fuel and my range was reduced from 70+ miles to 55 miles.
Bigger cc = engine sucks in harder = same size or smaller jets.
Maybe in a motor tuned for drag racing only, you will need larger jets to accomodate for the other mods.
On my KDX, the jetting was like 2% leaner but it would suck in 20% more air/fuel each intake stroke.
BTW, I'm not a fan of big bores, especially if you need to remove the power valve.
You will probably end up doing extensive tests and tuning to get the motor to run the way you want it to. Then you may find that you are stuck with huge gains in one area, at the expense of others (my old 240 would not rev out like a stock 200, but made great low end). Your usable rpm range may be much shorter, and even though the bike will be stronger in that range, it may be inferior overall. Basically, be prepared to throw lots of money at it to get it to work they way you want it to. Custom porting and finding the right pipe are pretty expensive things to do trial and error with.