This is what I would do,but first I will tell that I have the px,cf1,280,145,I have an improved 99 670HO that I run on the ice,I use the 145 alot because the profile is close to the 287 but better engagement and a little steeper for more shift rpm,the 280 and px are very similar but I find with testing that the 280 falls off in the middle where the px is better in the middle.the cf1 works great too but for the price I would try those other ramps first because the difference isn't alot but the difference in your pocket book will be more.
You can make anyone of these ramps work in your sled with the right testing,pin weight and helix's will improve your performance too.
I have friends that run 700's and they are all working with these ramps.
ROTAX POWER ALL THE WAY