local parts store sells a 600cfm holley carb with vac advanced secondaries and electric choke for 199.99$. would i see good performance from this carb? everyones been saying get a road demon but it looks like it would be tooooo much carb for a 305

Should work just fine on your engine.

would it be enough for a mild 350?

Works fine for me. And you can always drop an extra $14 for the "quick change" kit and the secondary springs. The lighter the spring, the sooner the secondaries open. This is a very noticeable difference SOTP, since the "stock" spring is the heaviest spring.

Awesome carb for you for the price. It all depends on your budget. Spend $100 more and you get a road demon, a really, really good carb, but that hundred could buy your intake manifold/ignition upgrade, etc. You see what I'm getting at.

That carb should work really well on a 305. If it were a 350 with more than 300 or so hp, I would get a 650 VS or a 600 DP.