You're getting into a fairly crowded area. The 3-12 SS is around $480, as best I can tell. You'll have to ask yourself what magnifications you are likely to actually be shooting at. For me, it wouldn't often be above 6X, normally less than that. If that is the case, large objectives don't do much for you.
To the left is a Swarovski Z6 1-6 x 24mm. Optically superb, this 30mm tactical scope goes for $1850 or so, retains a 4mm exit pupil throughout its zoom range, and you'll note that this optic has what many might think is a diminutive 24mm objective. Can you use larger than a 4mm exit pupil?
Reticle selection has a lot to do with it, for in extreme low light running out of reticle is more the issue than running out of image. One of the very best scopes I've used recently, for low light, is a Minox ZA-5 1.5-8 x 32 with a German #4.
Beyond that, illuminated reticles can be a big plus. The Hawke Endurance 30 3-12 x 50 is very, very good in extreme low-light-- 30mm tube, L4 illuminated reticle, and something like $340.
My favorite low-light scope, the Burris Euro Diamond 1.5 - 6, is discontinued. There is also the Black Diamond 3-12 x 50, new for 2011. I have one on it's way, but haven't seen it as of yet. That's a higher price point than the SS, but it has an illuminated reticle.