I have a 12 oz now. It takes 63 cranks to fill it and after I finish the round I only put 13 cranks back in it with a Thunder Tiger Pro .61. It's on a Super Kaos at 7.5 lbs and I use throtle management so I don't think a 6 oz with an OS .55 is too far out IF it's flown in the same maner and has the same weight which for the DB I think I'm right on spot. However I based that on the TT Pro which is an work horse that is broken in and a plane with a fat airfoil and can tollerate throttle management. I think the DB will be fine but not the Vertigo. Based on what I've heard about the Phoenix I'll be looking at a Novarossi or Jett or something like that. It's all going to come down to weight. We can get a DB to 6 - 6.5 lbs so that opens up a lot more oportunity IMO. Time will tell but I'll share the info.
Plus with a bladder tank you can use close to 100% of the fuel. The 6 oz 'snaps' into the canopy so with a little silicone it should be out of the way to put a 4 oz tank on the CG as a header tank.
I do respect your opinion Jim and you voiced something that keeps echoing in my head. I'm just guessing till I get it in the air...keep'er high!