You can pick up fixed sprockets for only a few quid, so you can always change the gearing cheaply. You will need a chain whip to do this, but you've probably got one if you've changed cassettes. One word of warning, however, is to take great care when threading a fixed sprocket - if you get it wrong the aluminium threads on the hub will ripped off by the steel threads of the sprocket and you'll need a new hub
I think the best thing is to buy the bike that you believe will meet your requirements, at a price that you find acceptable. The gear that you think you need now, might not be the one you find yourself riding in three months time.
On the subject of gears, I rode 52 x 15 fixed on the road at one stage. It was a very long time ago, and it was, (look away now, Travs,), on the A38 between Lichfield and Derby. I was very young and very stupid then; now I'm just older