Choosing the right carb

Sounds like most of you guys are leaning towards the 750. I understand that track times would be better with a larger carb, but this is a street only car. But it sounds like most think i'd be better off even on the low end with a 750? Sorry i'm new to this...

My reasons for wanting to try a different carb has a lot to due with the fact I AM so new to this. I've played with the holley vaccum secondaries quite a bit, new diaphram, quick spring change kit, lighter springs, heavier springs. Using the paper clip test my secondaries never seem to open much at all.
There is also a bad stumble just after idle till ~2k rpm, then it takes off. The thing I havent messed around with is the squirter nozzle and pump cam. But i'm not convinced that is it because I can feather the throttle right around the bog and it continues to run rough right there even after the initial acceleration off idle.

I've had a 6.5 power valve in it and now have a 9.5, I think I noticed a bit of difference after the switch, but its not quite there, I don't think.
I was also under the impression that without a mechanical carb with my 4 speed i'd be leaving some performence/drivablitity on the table. I guess i'm a bit quilty of having the 'just throw $$ at it to make it better' mentality.

initial timings at like 16 BUT I run my vacuum advance off of manifold vacuum so it idles with close to 30 and I allow 18 in my MSD distributor.

best vacuum readings I can get at idle are just shy of 12"