The scope I got (Zeiss conquest 4.5-14x50) was by far the most expensive scope I've ever bought, the next best scope I own is a VXII. I looked at several scopes in this price range, and I talked to several people. Everyone said Ziess was amazing and they say it's even more amazing in low light conditions..
That being said I figured with the 50mm objective, the light gathering ability would be maximized (even at higher powers). I just figured if I was gonna spring for a Zeiss I might as well go all out and get the larger bell. Once I made that decision I was prepared to spend around $800. But like I said before, I got a great deal on ebay. There is another one for sale, just like it, by the same seller right now. Item number 360029413966.
This is just my $.02
You buy what works for you, but I thought you might like to hear my experience since I just got done shopping for nearly the same scope you are shopping for.
I wish I could tell you how it performs but I haven't used it yet. I'm waiting for my rings to come in the mail. All I've done is look through it out the back window.. it's very clear, a very excellent scope.