Actually, that carb has secondaries that come on as far as the engine requires, so within reason you aren't going to over-carb. However, the smaller the CFM the smaller the primaries so the better the part-throttle response and metering, therefore potentially better MPG.

The other E'brock series, the Thunder, is the old Carter AVS, which stands for Air Valve Secondaries, and it has adjustable secondaries so you can easily tune when they come in. The Performer series is the AFB, which stands for Aluminum Four Barrel, and it was the go-to carb for many of us "back in the day". At least those of us who weren't into the Holley "stuff".