the nova is almost double of what the OS costs.

on a large permanent track, the nova will kill the OS, but on a small track, and with beginner/intermiediate skills the power difference won't be noticed, so go the OS. I JUST NOTICED YOU SAID OS SPEED, just go with the standard OS TZ dude... , you can get 2 OS TZ 3 ports for the price of one speed, or just go the 5 port OS TZ, mad engine

the nova is the motor of choice at the moment for most high end racers on fast flowing high grip/ or large tracks. Sirio is also a great engine, but again, if you race on a small track save the cash, go with the OS.

i'd recommend the novarossi 2630 pipe with the medium or long header. This pipe i found, frees up the engine and gives excellent punch as well as top end.