I used an 8.1 for about a Year, and I really liked the marker in general. I play mostly rec ball with a good mix of speedballers renters and tippmann guys. I ran with five mags on a chest rig. A few months ago I got the chance to trade straight up for a tpx with eleven mags. I decided to give it a try and ill never look back. Both markers shoot very well, and ergos are down to personal preference. However, the weight of the mags is SO much less with the tpx! I use nine mags total and honestly barely notice them, whereas the Tiberius mags really affected my movement. Almost as important is the shape of the mags; the tpx mags are a smaller, more uniform shape, which makes finding/using a rig much easier. Since I'm not a super stealthy "five kills with seven shots" sharpshooting pistolero, the choice to go with a lighter, more comfortable setup for a lot of paint was a no-brainer.
Don't be nervous about the co2 changes on the tpx, they're incredibly easy and fast after even just a few games with the marker.
If you Only plan to carry two or three mags per game, I feel the Tiberius swings back into favor since you know you'll always have air in each mag when you slap it in.
Proud member of the Phantom Lords.
Tippmann TPX, CCM T2, Empire Axe