My Astro 40D from Central DS still performs well.. cooled and spectrum modified. I personally wouldn't get a spectrum enhanced camera without cooling.. makes it a much more powerful camera.
It will take them awhile to develop the mod (4-7 months apparently), but a cooled and spectrum enhanced 6D would be a seriously nice camera at a not too scary price.
Right not you could buy a second-hand 5D Mark II and get it modded for a total under $3000. Not bad for a full frame sensor. At the other end of the scale, a modded 1100D would be a bargain and likely perform better than my Astro 40D.
http://www.centralds.net/cam/?page_id=5308
Phil