...as far as the body goes I do like the d80 but the iso performance on the d300 is much better the d80 seems to be hit or miss above 800. I tend to shoot indoors sometimes and even with my 50mm at 1.8 I still sometimes have to crank up the iso. Another thing is I like the feel of the d300 much better. The d80 is just a tad too small I feel and the size and weight of the d300 just feels much nicer in my hands. The 51 focus points on the d300 is also a plus for me as there are many times I have to move the camera to get it focused on what I want and I feel that I loose some sharpness doing this.
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I agree with what you say about the D80 in terms of ISO and AF. Size and weight in your hands is subjective of course. The D80 was right for me compared with the (at the time) D200, but I'm a strong believer is getting a camera that feels good and handles how you want it.
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As far as the 85mm goes. I am starting to get more into portraiture Ive only posted one on flickr but I do have more that I havent posted. From what ive heard the 85mm is the best portrait lens there is. I dont mind my 50mm for this it just seems that to get a nice tight headshot you need to get a little close to the subject and my concern about this is when shooting with strobes I dont know if being that close is the best idea since it may effect the lighting.
Well, you may only be just getting into portraiture but I think there's also quite a few of your photos, or at least the style/genre, that lend themselves to using an 85mm. The 50mm 1.8 is a great lens, and IMO without doubt the best value lens in the Nikon range, but it is only a 75mm equivalent, which is definitely at the very short end of the portrait range.
Personally, I'd usually go for glass rather than body. I take your points on the body issues but you don't seem *that* dissatisfied with the D80.
I think in your situation ideally I'd try and borrow an 85 or 90mm lens and see how much you end up using it before laying the cash down. Or even borrow a zoom that covers 85mm and keep it on that focal length (I know a zoom won't give you the depth of field of the 1.8).
I guess what it boils down to is, buying an 85mm will take you into areas that you're not currently in, whereas a D300 will let you keep doing what you're doing now, but better.