I haven't used the Sigma 120-300 f2.8 on Epic yet - but I have read some reviews of the lens from still shooters and they were really positive. The reports were that the build is solid, contrast is very good, the lens is quite crisp. It is wildlife and sports shooters who wrote the reviews. The lens costs $3,200 on B&H. Link: http://www.bhphotovideo.com/c/produc...2_8_EX_DG.html
The lens weighs just 6.5 pounds and is only 11.4" long.
Add in a 1.4x and you'd have a 168-420 f4 zoom (on FF35). Add in a 2x and you'd have a 240-600 f5.6 zoom (on FF35).
I've been thinking of testing out the above on Epic for sports and wildlife shooting for months now - but haven't gotten around to it.
As I remember, Red has tested out many Sigma lenses on Epic and entered them into the Red database. You might just check with Red to see if they've tested the Sigma 120-300 on Epic.
I've been using Miller tripods since August 2007 with my Red cameras. I'm now sponsored by Miller, so for mobile lightweight Epic tripod setups, I use the Miller Compass 25 head, in tandem with the Miler Solo 1505 spreader-less CF legs. The head has excellent action, the combo weighs just 13 pounds, and the head will support up to 31 pounds. We tested a Compass 25 head with Epic M 0008 clear back in March, using Ketch's spreader-less Gitzo legs. The results were excellent.
Miller Compass 25/Solo 1505 CF combo link: http://www.millertripods.com/product...3D2%26page%3D3
Hope the above info helps you out...