Not Ranked
Don't forget about the different brands. The OP isn't just comparing vacuum vs. mechanical secondary. There is a noticeable difference between a base Holley and a high end carburetor like a QFT or a Holley Pro Series.
I am not familiar with that specific QFT carburetor, but I have a home-built carburetor made with a Proform main body and QFT internals. I put this together several years ago before you could buy a QFT carburetor.
The QFT parts are top notch. For instance, the metering blocks have several emulsion channels with changeable "jets". It allows you to tune the carburetor better, plus it seems to be much smoother. I have removed a brand new carburetor and replaced it with my carburetor and the engine nearly always ran better. I have done this on a 351C, a 428FE, and 2 different 454s.
So, I would also consider a brand new QFT vacuum secondary carburetor with or without an electric choke.
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