I think the "k" rating refers to the rpm's at the clutch, and not at the engine. All these shops have different ratings, but I found the mid size springs from most of them to work the best. I also have 5.5gr Malossi rollers in my set up. I tried 7's when I first set this scoot up, and did not get into the power band on the pipe. The whole idea of the rollers is to tune to the desired running rpm's. I believe I top out around 11'500-12'000. 3'500 is where i BARELY roll, and 7-8'000 is where the clutch really locks up. Bad for fuel economy, but great for riding. With your kit being slightly larger I think 6ish would get you on it. But it all depends on where your kit makes it's peak power. Mine comes in around 9'000, I couldn't guess yours. The rollers will be trial, and error just like the jets. The factory springs I assume come in around 800 at the clutch.