Eyebedam, go ahead and buy those 300 watt panels and see if they work for you- I presently have a flower tent with 2 x 300 watt Galaxyhydros I got from amazon for $89.99(now theyre 79.99) and I average 25-35 grams per plant, using Sensibloom a/b, and floranova(molasses based fert) with a bit of Beastiebloomz for an added mid to late flower kick. I have a separate room for veg, and I've recently switched over to those cheap Chinese BLUE LED light panels - they were cheap enough that my grow buddy and I got a few as an experiment, got good veg growth and we've both switched to using them exclusively(switched from a 4 foot 8 bulb T5 fixture and growth has increased, with more foliage).
As the Seamaiden could attest, I have a plethora of MH ballasts and VHO ballasts and fixtures leftover from my reefkeeping days(I run LEDs over my tanks now too), and had nothing but problems, even with a borrowed HPS- everyone has their own methods tried and true.
Read everything as a guideline, take nothing as gospel, and develop your own methods via trial and error.