When cold my FE428 idles at about 650~ and then when the engine and
oil warm up the idle is at 750 to 800. At these low idle speeds the engine is turning slow and the exhaust note is very pleasant and rumbly. The down side of this low idle is when cold at 650 RPM or so, the idle is rough and I do get some shake but this leaves when the idle rises to the 700+ range as the engine warms.
My engine's carburetor (Holley 850 Double Pumper 4150) has no choke and as such when the engine is cold I have to attend the engine with pusling the gas pedal. If I just started it up and took my foot off the gas it would NOT idle but die. I have to use my gas pedal as a choke as it were. This sounds crude (it is) but works out well in practice.
I have 3.31 rear end so to drive the car slow (in a parking lot for instance), I do need the low RPMs. When I had the RPMs higher in the 1000 range, I had to feather the clutch to do slow driving and since my clutch is a racing type (it is either IN or OUT) feathering the clutch is nearly impossible.
Hope this helps?