I put 440source stealth heads on my 440. Left the stock cast iron intake on there. So the heads are aluminum but unlike stock heads, they don't have the heated exhaust crossover. I did notice it takes 5 minutes longer for the choke to open now on a cold day than it did before. I run a thermoquad, stock choke without the electric assist part hooked up, just the stock thermostatically operated coil running the choke. I know it takes about 5 minutes longer because I drive the car to work daily and I'm closer to work by the time the choke fully opens and it drops to base idle speed at a stop. Cold driveability is no worse really, just have to drive that extra few minutes before the choke fully opens and I can feel it's warmed up. I bet if I had an aluminum intake on it, the choke would open up faster just because the aluminum will heat up quicker from engine heat than the cast iron. It's usually in the -10 to -15*c range before I pack it away for the winter. Once the intake has warmed up, it's just as fine running as it was before.