Ive owned both the ss 5800 and the 5.5r. Only reason i can see for buying the 6.5 over the 5.5 is the 6.5 should be a little more 'tame' for offroad use. anyone good at using the slipper clutch/radio trim/throttle control will be fine using the 5.5. The GTB is definately smoother on the throttle. could hardly tell the difference between driving a 5.5 or a brushed mod on carpet TC. Id guess novak wont release the 5800 and GTB as a combo as the 5800 is an outdated motor, and i believe u can purchase the 5800 motor seperately for rather cheap price.
Yes you can de-tune any system, if you have a radio which you can adjust end points. And i 'think' the GTB can be programmed as you suggest also. Dont quote me on that tho. Ive never needed to de-tune my 5.5
