[Tony]

I've messed with inlines for quite a few years now.Not the later 230-292 Chevy types but the older GMC 302 inline 6.
The last one I built recently was a 302 with a moderate cam(215 degrees at .050. lift),tube headers,9.25 actual compression ,water heated Clifford 4 bbl intake.This combo makes about 230 hp at 4500 rpm,maybe 320 lbs. of torque at 3000 rpm .I found through a lot of road testing and carb rejetting that a 400 cfm carb is all this engine needs.Larger cfm carbs din't help performance.This engine is in a 2900 lbs 37 Chevy truck with 5 speed.
I also found that this engine needs a richer full throttle mixture than a typical V-8,especially at the torque peak around 3000 rpm.As the engine winds up near peak power the mixture could be a little leaner,not exactly possible with typical 4 bbls,so it's a compromise.
I don't know if my experience can apply to the later inline 6's but it should be somewhat similar.
I would say a larger carb works better at higher rpm's. For street driving with 250 cubic inches ,5000 rpm maximum,350 cfm should be fine.It's best in my opinion to use a smaller carb gving better throttle response and economy at the rpm range normally seen and give up a little on top end that's rarely seen.The Clifford intake has fairly large runners and under carb plenum making the carb bigger than it is so to speak.
It's your engine,tune it the way you want is the only way to know for sure.