The OP stated low light pics are important. The OP also stated the interest in a f1.4 lens, obviously to get the best low light performance. The cost of the lens is a big variable.
I feel the newer bodies offer so much better ISO performance, that the answer given should show the best combination of body/lens for the money.
I am only familiar with the cameras I have owned, a D70s and a D7000. Based on my knowledge, I would have to recommend a D7000 and a 50mm f1.8.
Yea, this is a few dollars more, but, averaged over a few years, the D7000 will blow away the older bodies, low light performance wise.
If the OP gave an exact budget, the answer could be simpler, but, that f1.4 lens throws a monkey wrench into the system selection consideration.
Now if bokeh is the reason for the mention of f1.4, maybe a different answer would come up.
Mmm, good point. A D3100 with a 50/1.4 is probably going to cost more than a D3200 or something like that, coupled with a 50/1.8. And the body's better ISO performance extends to all lenses used with it, plus you get other improvements along with the better body.
