RE: 2 Klunk/Pump Setup
Nope. Actually noticed the opposite and in a situation where the engine runs were VERY well monitored.
Tank plumbing used to be a very hot topic in CL stunt. Guys argued the best plumbing arrangement for years. And they often swapped out tanks quicker than they changed their shorts. And they'd swap them out from one flight to the next, so the test proceedure was one in which for once there was REALLY only one variable changed with an immediate re-test. And the engine run time was super critical, so the testing included a very strict check for how long the engine ran. It was basically life-or-death to have the engine run long enought to get through the cloverleaf but not run over the maximum flight length.
It didn't always happen that a uniflow gave better "mileage", but they often did.
Like everything else, it seemed to depend on a number of other things. What was the "other" tank? Did the engine's carburation or fuel draw or centerline or color or age or timing or prop nut size or..... whatever "like" any tank's draw better than it liked the other tank's draw or whatever.
BTW, put a good fuel filter close to the needle valve and you'll often see less differences in mileage, and more uniformity in about every aspect of how your engine is running. The filter "combs" out any foaming that gets that far. Sometimes....