I don't have any experience with Steve's LED's. Heatsinks seem to be a bit of personal choice.
If it's up in a hood, you could probably get away with almost any piece of stock aluminum. No real need IMO for a factory heatsink. There's lots of examples of guys using square tubing and stuff.
I also found that trying to get a perfect mix of X amount of RB LED's to X amount of NW LED's to acquire a 14K MH look is kind of like finding a needle in a haystack. I tend to subscribe to overbuilding the fixture but have the different colours on dimmers and dial in the colour you want.
And in all the reading I've done about LED fixtures (and believe me, I've read tons!) you have to go as full a spectrum as you can afford. LED's emit a VERY narrow spectrum of light compared to MH. And I don't think we fully understand the need for which parts of the spectrum are needed for optimal growth and appearance. So the closer we can fill that spectrum in, the better odds we have of supplying what our tanks inhabitants need.
On my fixtures I run RB, NW,CW, OCW (red, green, blue), 405nm TV, and 430nm TV and I still don't think I've got the spectrum in full. Thus I chose a heatsink that doesn't permanently mount the LED's so I can fill in and replace LED's as the technology and our understanding progresses. So far, it's grown everything I've put under it except some purple poccilipora. No idea why, it just won't grow.
Anyway, sorry if that wandered off your questions there, it's fairly early and still drinking my 1st cup of coffee
