sorry, selective quoting to change the emphasis ofwhat somebody said is a pet hate of mine lol, im sure, form our past converations that you didnt do it on purpose..
the thing with the d40 though, it isnt JUST the incompatibility with certain lenses, there are also "cut downs" like for example the need to go into menu mode to change more things.
I think, if you read all posts regarding what lens, the "nifty 50" is a massively favourite lens, the loss of that (or at least AF on it) would be a big blow
Of the two the d50 has to be said, it is superior, the D40x may be a different story because of the extra MP sensor, but I believe the OP was just talking the D40 and not the X model
I had my D50 since last may I think it was, and there wasnt a day that went by that I wasnt pleased that I chose it and didnt go for a D40 (I did try a d40 in a shop but it felt like a toy camera)
I changed today to my D70, and one of the reasons (not the main one, but a consideration) is that i have specific camera insurance, and if anything happened to my D50 then they would try and palm a D40 on me (as the replacement model) if anything happens to my D70 then i would probably get a D80 as a replacement
the other thing to think about ( and this is more of a personal thing and not directed at any body ) is that with the popularity of photography, DSLRs (bodies and kits) have become very affordable, and a lot of people who are on a much tighter budget (like myself) have stepped into the hobby.
you can easily spend thousands on gettign your kit together, and that can be very difficult to do in one go, the easy option is to get on popular auction sites and buy older lenses to keep you going untill you can afford a new better lens, or in fact when you first get into the hobby, untill you find you niche and decide on what lens you really need.
the 50 - 500 is £568 ( according to the quick search I have just done) and that is a budget lens, do you see where i am meandering to with this thought train lol
the point is moot for this thread because TheBear has said he going for the D50