With regard to downsiding doubles properly, the key with this, is you may not need to be going top speed to downside it properly. Our track has a section that features a large table top, followed by a close triple. The floor it and see huge air time guys normally, hit the table top and land on the flat part of the track right before the triple, thus they are thrown out of balance and crash on the triple.
The guys that use throttle control, determine the amount of speed necessary to get the car over the table top, downside it, and hit the throttle for triple. Remember if your car is in the air it can't accelerate. And by downsiding a jump you can carry more momentum and pass cars quicker. I have often times passed cars on this section of our track simply by timing my jumps better and being able to overtake them in mid air, as my car has more speed going into the triple then theirs.
The other important thing. Between rounds, always inspect the faces of jumps. If the track is outdoors and dry, the face of the jump will change during the day. Sometimes it's necessary to change your line to avoid holes that will send your car into a cartwheel. Indoors it happens more if gas cars are also running the course. If you see a hole in the track or the crown of a jump gets a dip in it, avoid that part otherwise your car will be launched sideways as the part that hits the normal part of the jump will have a compressed suspension, but the side that hits the hole, will lose its compression entirely thus sending your car into the air sideways.
Hope this helps.
Paul