Like Dusty said "...you have to keep your foot out of the secondaries...". And what BVA said "The carb will only let through as much air through the secondaries as the engine requires, assuming everything is dialed in correctly. It's more carb than the engine needs, but no worries considering how the carb actually works. On the highway it's all primaries, so tune those as lean and with as much timing as you can without pinging."

Also, IIRC, Vizard said that in theory, there is no such thing as a carburetor that is too big. BUT, I don't think I would put a Dominator on my engine and expect to get it dialed in.

I have a 465 with vacuum secondaries on my engine...I have had a 450 Economizer on it which comes with mechanical secondaries. They both virtually run the same except for the lack of tuning capability of the Economizer which is pretty much limited to jet changes...it takes Weber jets. With either carb the secondaries aren't effective until the engine speed gets to around 3000 rpm MOL. It can be made to bog with the 450 at lower engine speeds because of the mechanical opening of the secondaries...it's all in the foot and knowing what the engine can handle. Vacuum or flow operated secondaries like on the Holley or Edelbrock or Qjet can be adjusted so that they will only allow what the engine can take. Ya just can't force-feed the engine more then it can handle without problems of driveability.

At some point each driver must take responsibility for their manner of driving and finding the manner that will result in the balance of mpg and performance that they want regardless of which carburetor they use.

Having said all the foregoing tripe, it's JMO that a spread bore carb like a Qjet or Holley 80555C with small primaries for the 98%+ driving one does and large adjustable secondaries for the "Exxon" moments would fit the bill on even an otherwise stock engine.