What to upgrade first....
I think I know the answer to this question and I think I've made my decision, but I'd be happy to have some input from some more experienced amateur photographers:
I've been a DSLR owner for about a year and a half now. I have a D3100 and two lenses; the 18-55 kit lens, which I almost never use, and a Nikon 70-300 4-5.6 VR ED, etc. etc. FX lens, which I use almost always. I've been saving up for awhile and have ~$3000 that are unnecessary to my continued existence otherwise, which I have earmarked for generic photography gear upgrade.
With the recent announcements from Nikon of the D4 and the D800, I've been drooling over those a bit but also thinking that there would probably be a lot of D3, D3s and D700's floating around used at pretty good prices, so I was considering trying to pick up one of those (or a D800 if I couldn't find just the right spectacular deal). My thinking on this has been with the D3 or D3s I would gain some flexibility in ISO that I am lacking on my D3100 and be able to take some shots that I miss now (well, actually sometimes I take them then curse them for being noisy at ISO 1600). Plus, I'd be getting a nice, weather sealed body so I don't have to freak out if I'm out and have forgotten to bring a plastic bag or something to cover my camera with and it starts to drizzle. I'm sure that I could keep a camera body like that for quite a while and it will still take fabulous photos for a long time. The flip side of the equation being that I lose the DX crop factor and therefore my 70-300 lens is a wider lens than I've been used to and that may or may not annoy me. And my 18-55 lens in that case stays glued to my D3100 since it is a DX lens and unusable on the FX camera.
My other thought was to get a Sigma 120-300 f/2.8 lens for about $3000 and a 1.4 or 2.0 TC and keep my D3100 for awhile longer (probably a year-ish). This would give me the flexibility of having a 120-300 with greater low light usability or add on the TC and have a 420 or 600 at f/5.6, plus retain some zoom capability. I'd also retain the crop factor of my DX camera so that as far as pixels on subject, that 600mm has the angle of view of a 960mm lens. Plus, since I'll most likely be able to continue to use the lens for many more years than the camera... that'll be a good thing.
So I'm leaning heavily towards the lens. Do you agree?