Go to the store and try both and see which one you like better. It's not about which one performs better, but which one matches your heart and style more.
Unless of course you believe that the photo is a product of the camera, instead of the photographer.
I had to make the same decision 4 months ago at the shop. I was all ready to pick up the 40D but after playing the two side by side and seeing how much better built is the D300 and confidence-inspiring, I ended up with the latter and $900 poorer. 4 months later, I still have absolutely zero regrets. It was additional money well spent.
wah...first dslr is d300/40d ah?
I started off with pentax k100 then d80 now d200.
Pls note this:If the purchase of the d300 means you cant buy good lenses then start off with an entry-lvl dslr.
For example,D300+nikon 55-200 will NEVER even get close to the IQ of D40+nikon 70-200mm
It shd be lens on 1st piority and body next. A good lens will last u for years but a good body will eventually get outdate in a year or 2. Entry levels DSLR cam come out with new model each year. Semi-pro will change in every 2-3 years. U will seldom see MkII or MkIII on pro lens.