Compared to the total weight of the bike and you combined, 3lbs is not much, and it's the combined weight that's going to slow you down going up those hills. The extra granny gear also doesn't add up to much though either. If you're keeping a decent cadence of 80 up those hills, you'd be going 0.5 mph slower in the 30 vs the 28.
So not much in it really. Pick the bike you enjoy riding the most!
As for 4500' being "not hilly" it really depends on how that is made up of course. I can ride a century and cover 4500ft and it be mostly flat around here (by PA standards), equally I can do 4500ft and have it kill me. Really depends on the grades of the climbs!