I like the predator, it's decent. My only complaints are
1) that the air filter is a crappy sponge instead of a paper filter. 2) The decals for the throttle/choke were peeling off out of the box.
It's worth the $100 though, they are pretty reliable. If you are worried about it breaking, just make sure you break it fast so you can get a new one within the return policy guidelines. If you want to break it slowly, just buy an extended warranty/replacement plan.... If you plan on not breaking it any time soon, just don't "mod" it, (which will make the engine wear out much faster than it should). You can, however, adjust the governor a little or buy a better exhaust/filter/carb/flywheel/... But by that time you could have bought a better motor with more "stock" power.
This is just my opinion below, modifying may be what you have your heart set on.
If you want more torque, buy a bigger engine or change the gearing.
If you want higher rpms, buy a dirt bike engine or a small motorcycle engine, or racing engine. These were all built for speed, without any mods.