To be honest for the price of a shaft4 you can get other barrels that perform just as well. Don't get me wrong, great barrel, But I'm not gonna be dropping £60 or more quid for 2 backs, seems a bit pointless. Like it has been said, a tube is a tube, what matters is the control bore length, and the bore of the barrel itself. I'm gonna suggest another barrel that might be an option for you- The Shadow Shake kit. 3 backs in varying bore sizes, pure carbon fibre tip (so its slightly lighter, if you are that incredibly worried about weight) and a velvet carry case to store it in. Comes to £95 retail or £85 for me. I started using them, god damn they were way better than my UltraLite. You've dropped some cash for it, and you get varying bores that you can match the paint to. Brilliant piece of kit, I use it all the time now.
At the end of the day, there's a lot of options- but then again, a tube is just a tube. How much can they differ? Pick what you like the looks of and one that people report shoots consistently.