...cuz it has to be able to run both MH and HPS, or you have to use a conversion bulb (I like the Sunm4st3r, meself) that will run in your existing HPS ballast. If your ballast can do both, then yeah, it's just a 'change of bulb'.

Running MH during veg should help reduce stretching to a minimum, but if ya just have to keep the HPS on 'em, you might try some Bushm4st3r additive which is supposed to help a bunch.

As to the heat issue, you just might need to vent a bit more and bring a bit more fresh air in. If you can't, at least move the air a lot, and don't let it go above 85 consistently, unless you can increase CO2.

If you want to use the Hortilux bulbs, just make sure they work with your ballast. Some digital ballasts apparently have problems with 'em, but there are fixes. There are also now bulbs being deliberately designed for digital ballasts, too

I am a fan of CFLs, mostly because of the fact that I can get replacements cheaply, on every street corner. They do make some heat, tho, when you get enough of 'em in there to count, and they're unfortunately not as efficient as what you already have. The Sunbl4st3r ones are in the range of Metal Halide efficiency (90+lumens per watt), but your HPS puts all of 'em down with 130+lumens/watt). I am currently running a garden in my livingroom that is approximately 2.5 square feet, and 12 CFL bulbs putting out 24,800 lumens in total.

You could 'supplement the spectrum of your HPS with some CFL or other flouros, just to help 'flesh things out', look for either 4100k or 6400-6500k colour temperature. T5HO are 90+ lumens/watt, and T8 can run around 100lumens/watt. CFLs are available everywhere, but I like the SB ones that give 2500 lumens for only 26w

Hope this helps!