What's the max amount of travel you guys think i could install on this kind of frame geometry? I have the same bike as the image. It comes with a suntour 100mm fork and a really stiff rear shock coil. The bike is designed for XC, but i would like to hit some bigger jumps on it. Aluminium frame. The bike model is Berg Trailrock 100x
I wouldn't consider anything over 140mm. beyond that, you're really messing up your geometry and endangering your frame.
Keep in mind that your frame's limits are really determined by how much you weigh. If you're 140 pounds, the frame will take much bigger jumps than if you're 240.
You say that the rear shock is really stiff. It seems there is an imbalance in stiffness between the front and rear suspensions. If you don't have the preload on your Suntour cranked all the way up, you should try doing so before upgrading.
You could fit 120mm, but you really shouldn't. You shouldn't even really be jumping on that bike shaped object.
Hitting bigger jumps does not require more suspension unless you are doing it on the kind of terrain which that bike is not capable of handling. Hitting bigger jumps only requires more technique.
If you are serious about getting into dirt jumping I would try to sell that bike, add some money, and get a 2nd hand dirt jump bike without any suspension and work on technique.