I used to run a 47/30 steel tank but due to an awesome friend am now running a 45/30 cf tank for my Spec-R. Out of a 45/45 you should get around 750-ish shots IIRC and the 68/45 bumps you up to around 1k-ish. The stock barrels are really nice. I just picked up a Deadly Winds 14" Fibur barrel with 3 inserts just waiting for it to get here which is the hardest part lol. Your set up sounds good though. Try different ones while at the field and see which feels better to you. My harness holds 5 pods but I only run 3 cause I like less weight and easy maneuverability.
DP G3 Spec-R - G4 Reg, Bob Long Cam Drive ASA, Deadly Winds 14" Fibur Barrel w/ inserts, Pure Energy 68/30 CF Tank & Empire Prophecy Z2 w/ Virtue Speedfeed
Dye I4 w/ Blue Ice Lens
Blood Clots, Sweat Dries, Bones Heal... Suck it up Princess