I have both the 5D and the D3 (and a R-D1, and a M8, and way too many film cameras). The D3 has 1 1/2 to 2 stops advantage in high-ISO noise performance. It focuses much faster (not that I really care, since I use a manual focus Zeiss ZF 50mm f/1.4 Planar with it), has a better viewfinder (I can manual focus with it as well as with my father's old F3) and it has a faster sustained frame rate. It is also much heavier. If Canon made an improved 5D with the same high-ISO performance, I would have gone with that. Ergonomics are a question of personal choice, I find both cameras to handle just fine.
I don't know what "film-like" means. Sure, the grain texture of specific B&W films like APX 100 or Tri-X (the old kind) printed on gelatin silver paper using an optical enlarger is inimitable, but as far as having a gradual shoulder in the highlights go, the superior dynamic range of the DSLRs allow you to do the same in post-processing. The only film that can match them is Velvia 50, Neopan 100 or Kodachrome 64.
The D300, I'm sorry to say, doesn't hold a candle to either in the image quality department. It may handle faster than the 5D, but the viewfinder is just as nasty as any other 1.6x crop DSLR. There's a reason why people always compare the D300 to the much cheaper 40D, and seldom to the 5D...
As to which one to get, if you want to extract the maximum performance in low light as I do (the M8 is a major disappointment in this regard, even with a Noctilux), and if you can afford it, get the D3. Nikon priced it very competitively because they had to make a big splash to get the PJ market back, and it is tremendous value. It blows the 1DmkIII completely out of the water, for instance, for a small premium, Nikon could easily have charged an extra $1000 for it and people would still line up to get the D3. Otherwise, the 5D is the best value for a serious amateur (or cash-strapped pro, or one who needs to go light).
Of course, availability of the camera is also an issue. Given Nikon's track record, I think it will take at least another year before the D3 is readily available. The 5D is available today. My friend at Calumet tells me it's by far their best-selling camera, there's a reason for that.