I would recommend going with the 6K because it will be more versatile.
The 2Ks might be fine for white limbo, but you may need a bit more fire power for darker colors that you want to pop or if you need to shoot at faster shutter speeds or use dark filters such as a polarizer.
I use nine 4K spacelights on our 30x60x17 cyc and find it to be barely enough for many shoots and not enough if I'm shooting around 1/100th sec.
The brand of our 4Ks is UltraLight. I think they only advertise the 2K and 6K, but you can ask for 4K. As a brand it is OK, but I think I would prefer the 6Ks from Mole-Richardson.
DP – Transvideo Studios
Mountain View, CA