3/8 tenex if spliced properly for an eye'n'eye fattens up to a little shy of 1/2". I've used 3/8 ultra tech, secured with double fishermans/overhanded noose. Works good, but if you're using a rope guide the polyester sheath melts off pretty quick. I've grown really fond of how the 5/16 HRC works with my Blaze. Only limitation is my fingers get closer, therefore warmer, to the rope on quick burns.
I cut the HRC to a length of 44" then tie double overhanded noose knots to secure to my biner. 44" gives me a nice short VT on Gold Streak, and an average length on Blaze.