With my experience I have found that not only do higher wattage diodes penetrate more (Which I understand you don't need as much in scrog, I use scrog and LST often as well) but they also cover more area and grow at a more vigorous rate. Of course you need to look at budget as well, but the smaller wattage diode lights still cost close to the same as the higher quality higher wattage diodes. Now there is the issue of quality. If you want good results you need to invest in a quality light, and there are a very limited amount of quality LED lights out there, and few offer a good spectrum of light, and few offer quality diodes (Cree, Epistar, etc...). Stay away from the Chinese cheapies, as you will be unhappy with the results and find yourself actually wasting your money. If you take a look at my journal as listed below, you will see that one SolarStorm 400w covers my LST'd plants quite well, and my growth far exceeds that of my former 3w diode light (357 Magnum). Overall cost of buying 2 lower powered lights will cost more than buying one higher powered light. You can find the SolarStorm 400w online for around $800 delivered, I paid $700 for my 357 Magnum (not Magnum +) and it only has half the wattage and half the coverage.
So my conclusion is this: Higher wattage diodes = More coverage area and much better penetration, which = Justification for buying higher power diode lights, which = Happier plants