I used a Big Shot plate system in my Camaro. It was good for 400 hp but would have killed my engine. I got 3 runs per bottle with it set at 275hp. I think a lot depends on what your engine can handle. If your sixty foots start dropping off, you may want to use less nitrous. Too much will bog you on the start line, blow your diff apart, break axles etc, or just f***k your engine - you know, detonation, torched heads, block, rings etc.
My Nova uses Speedtech foggers, two systems. I hit the first system with 400 hp and the 2nd at between .4 and 1 sec after launch with 300hp. I was running one bottle but pressure was dropping off too much. I plumbed up a second bottle for the second system.
I get two runs from each bottle before changing. If you let the bottle get too empty, there will be a fast drop off in pressure during the run. If pressure drops below about 850 lbs, the entire contents turns to gas and is no good. By the way, anything over 1060 pounds will be all gas too. You need to be between 950 and 1000 lbs to ensure its all liquid and you have enough pressure to run the systems properly.
Good luck.