I wil try to help. All carbs jet the same. The difference carb to carb is how much and where the jets overlap.
I haven't read all the posts but it sounded like you found too lean on the mains. Just richer than too lean is perfect on the mains. Don't go back too rich. A bigger needle jet (richer) mainly effects just off idle to quarter throttle. A different base diameter jet needle does the same thing. The other biggie is the slide angle and they effect about the same range. BIG mileage changers since you are in these jets during a lot of cruise. Slides are expensive but you can make them leaner with a file. The tricky part is matching them on multi-cylinder bikes.
Idle jets do not turn off out of their effective range. Too rich an idle jet WILL effect mileage.
Part of the trick jetting just off idle is that different combo's of slide angle/needle jets/jet needles/idle jets do different things. To really find out what works best, you have to try a lot of different combo's. It's a lot of time and a lot of jets (times two!).
Like I always advise about Bings, it says right in the Sudco manual somewhere that needle jets are crucial. It really is true with Dell's too. That and the slide angle makes all the difference in the world. Good luck and I hope I am not poking the bear!