Wow, thanks man! That certainly clears things up.http://current-usa.com/wp-content/uploads/2015/04/Satellite-Comparison-V3.pdf Model Comparison Chart
I own two Current USA LED +Pros and I love them. The main difference between the + and the +Pro is the potential light output. With my +Pros at full power my tanks are brilliantly illuminated and my fish look absolutely spectacular, but if I leave the light one full power I end up with uncontrollable algae problems. Luckily you can customise the light output of the white, red, green, and blue LEDs individually to suite your needs. I usually run mine at 40% power in order to avoid algae outbreaks but everyone's light needs are different. The +Pro also comes with a 24hr timer which has a nice 15 minute ramp up and ramp down feature which I like because the livestock you keep aren't subjected to sudden blast of bright light every morning and then sudden darkness every night.
Ultimately the size of light you need will depend on your plant arrangement and tank size, I'm assuming 36" if your considering between these two sizes. If you absolutely have to get a smaller light in order to get the +Pro then I would opt for the lower model in the 36"-48" because it would provide me with more light coverage. Again it totally depends on your tank, if you only have plants in one area of it then you might not need all 36" of light coverage. The + is probably enough light for any tank I've ever seen and I might go as far as to call the +Pro overkill, but sometimes when people come over its nice to turn the LEDs all the way up to show off.