(I understand that you are working on a project bike, and it may be a matter of sh(well you know the rest of this word) and giggles, but I have noticed a lot of people wanting to upgrade the 250 (on this forum and others). So I figured that I would finally spread my share of knowledge on this matter. It really won't answer your question totally, but it is a rant, none the less.)
All I have done is a K&N filter (PN# KA-2508
). Two brothers does make an exhaust system
which will bring you up to about 31HP. Im sure after the K&N Filter and a carb jet kit, you will be pushing 35HP (Disclaimer: I am not a pro, I could be wrong). You could then add a wet shot of NOS and that may get you close to your target.
Is it worth it? You will have spent over a grand on these upgrades.
Instead of modding the bike, I think I am going to get a Ninja ZX6. I love my 250R, as it is my first bike, but I realize that it IS my first bike. It has done its job very well (helping me learn how to ride while avoiding death.)
My plan of action (within the next year).
1. Sell the 250R to a good home - either craigslist or ebay (trading in=bending over)
2. Go to the kawi dealer and sign the papers on a ZX6 (same color as my 250, super atomic bright green)
I understand that modding an existing bike instead of purchasing a bigger bike may be a matter of money, but there are plenty of fairly new, nice bikes on craigslist. Modding the 250 for only performance is a false economy. Not only are you going to trash the resale value of the bike, but it is going to wear out the engine much faster, cause rideability issues, wear out rear tires faster,... well the bottom line is: It is not cost effective to upgrade the 250 vs. buying a bigger bike.