Hi Guest. Welcome to the new forums. All of your posts and personal messages have been migrated. Attachments (i.e. images) and The (Old) Classifieds have been wiped.
The old forums will be available for a couple of weeks should you wish to grab old images or classifieds listings content. Go Here
If you have any issues please post about them in the Forum Feedback thread: Go Here
As for its internals I could only guess (am on my mobile ATM).
If it is short stroked, its possibly a low ratio/high speed set up, with a high torque motor, or it could be dual sector (I think that's right) gearing.
When I finally get a new 8mm gearbox for my mp5k, I plan on 13:1 gearing, lonex a2 motor, with a M120 spring, which should see me to 300fps, and 20-25bb/sec. Don't know if I will have to short stroke it or not yet.
As for the best motor, from my reading, systema (£80+) then lonex (£50+)