There is a marked difference between SSR2 and 2.5, so you may want to go with 2.5 if this is an option. However, if you are able to get the job done with SSR2, as long as you've got the time, I'd say use it. Go the least aggressive route possibe!
(You really shouldn't need SSR3-It's POTENT!! Compared to SSR1&2, it's like liquid sandpaper!

)
One thought about the passes made, are you fully working the polish before removing it? Some people tend to go a bit fast if they aren't used to the PC or polishes. If you are basically spreading the polish, going over the area once or twice after and then wiping off the residue, taking all of 1-2 min. per panel, you likely aren't working it well enough.
You don't need to worry about burning the paint with a PC 7336 as you would with a rotary buffer, so you can take some time and "experiment" with the speeds/time in relative safety.
Here's a very good post on using the PC:
http://poorboysworld.net/board/viewtopic.php?t=65
As for going to a different pad, my understanding of the Edge 2K is that the orange is more aggressive than the light green pad, so you'd be going less aggressive by switching to the light green. With this in mind, I would caution you about using the yellow cutting pad, as it *typically* leaves a haze that will require follow-up buffing with less aggressive pads and polishes, so, in your case, since you are able to get the marring gone in 3 passes with 1 pad/product, you likely wouldn't save yourself any time going this route.
You can go from SSR1 to the LSP without going to PP between.
Hope this helps!