I agree, six. My coop is also 4X6, my run 8X13. They are comfy in the coop, plenty of elbow room. They are 11 weeks old now, and will probably chunk up some more. and there will still be room for them.
I wouldn't want 6 birds in a 48 sq. foot run unless they'd be out for a few hours each day freeranging. Other wise I'd say a MAX of 5, and 4 would be even better, especially since you're in a place that gets winters. The more space you have in your housing, the better off your birds will be come the cold/snow season.
That's the generally recognized minimums suggested. Lesser measurements come into play, because you have to factor in commercial chicken industry standards (which is pretty much turn around room only inside, and no outside space for most). So compared to THAT - 2-3 ft. of indoor space and 5-8 ft. of run space seems roomy. It's not roomy for normal chicken behavior, but in comparision it must seem that way.
For somewhat normal chicken behavior, limabean's numbers are what is most often quoted. Of course many chicken owners give a lot more than that. Mild winter areas can get by with a really small indoor space, as the chickens are literally never indoors except to lay and egg and roost, so roost space is important. For those folks, a really large run is more important. But in areas that get winters, and therefore the birds spend quite a bit of time indoors for a few months, 6-10 sq. ft of indoor space (per bird) is not out of the question.