I also like caps on, though I never liked the standard speed caps, as they fell off all the time when the cap was off and loose.
The standard 'leather punch a hole in the cap and push a knotted rubberband through', cheapo method was always my favorite until I quit using tubes.
Whether stuck back in a loop empty or tossed in a dump pouch, they always came out ready to go.
My method for carry was to have a basic rig that I always used to maximize my comfort and speed, then to have 'mule' packs that I could reload my harness with:
I bought 3 of these. I could alice clip(they had belt attachment too) 2 of them back to back. This gave me 40 tubes and 20 co2. At big games, when I hit the deadzone in a hurry to get back to battle, I could dump my empties and grab the shoulder pack, reload my whole 20 tube rig and have the stuff to do it all over again.
When I was speedloading my P68SC, I would have the tube in my left hand still capped, with the top between the ring and middle finger and the rest sticking out the bottom of my hand. This gave me index finger, middle finger and thumb to pull the plug. Holding the plug with my index, middle and thumb, I would push the bottom of the tube against my side, sliding it up through the loop of my thumb and index until the tube stuck above the plug. As I did this I rolled the plug between the tube and my fingers freeing my thumb. I'd pop the top of the tube with my thumb and pour in the paint. Rolling the plug and tube in my hand to drop the tube, I'd replace the plug.
It sounds more complicated than it is, I hope it makes sense.