To be honest, Id just sack it off and get a decent all round hardtail
I’ve been down the short travel full sus route (Old Specialized sx) and although it was a bit more comfortable and provided a bit more grip on the rough stuff, Im not sure whether it was actually any quicker.
The big difference comes when you do jumps (im assuming you mean properish type jumps rather than undulations in the trail), they just soak far to much up and just seem a bit too unpredictable. If you get one with an air shock you could pump it up really hard but then its sort of pointless having the rear sus in the first place.
My SX also seemed to be a flexy thing when jumping aswell (probably a common thing with 4 bar linkages) I remember doing one of the hip jumps at Glentress (not particularly extreme, I know) and it felt like the back wheel was by my side as I was turning and pumping the take off. Horrible. My single pivot patriot seemed a bit stiffer though, although it felt really sluggish on small jumps (like those at glentress) and was a bitch to manual and bunnyhop.
You have lots of travel in your legs for absorbing bad landings, 4 inches of travel doesnt make much difference.
There are a few advantages to having a little bit of travel, but for general larking about (jumps/drops and a few bikes rides) you cant get any better than a decent hardtail with 4/5 inches of travel at the front and decent geometry.