CarlD is right on for this one. The most efficient panel setup may see less than a 2 degree rise from the panels, but if you're turning over 40gpm vs 10 degrees at 5gpm, that's almost twice as much HEAT going into the pool. Thats why many permanent installations push for as many panels as possible, not only do you get a larger surface area, but you can put through a lot more water. I just saw JohnT's post, I would have to agree that it is probably that or more.

But, if your pool is at or close to where you want it to be, I like the idea of slowing it down and getting a warm rush from the returns!