You have some good points, I don't know enough about Vista except that there are a lot of complaints on the internet, even this thread alone. The only Vista I heard worth having is Ultimate. I have no problem with XP.
I can see why you asked the questions, rereading my post seems to have no point, clearly I was thinking ahead of my typing and not including all of my thoughts.
The question I missed asking is, is it worth having Vista, especially the lowest end of their range or should I keep XP? which then lends itself to the rest of my post.
Part of the reason for upgrading the machine is to get better performance, but if the operating system negates the hardware upgrades then it wouold seem to be a pointless purchase.
As to the directX 10 question, I know that compatible graphics cards have improved performance as it allows essentially multi core processing and hence utilizes the card to it's best potential. DirectX 10 was initially a Vista specific version of DirectX. If I'm upgrading the machine and graphics card to be compatible with DirectX 10 then I would like to make sure it is used for this capability. I've heard and read rumour that there is a DirectX 10 for XP but I've not found any evidence yet. So if there isn't DirectX 10 for XP then my question is answered and I'll need to see what I can do with Vista. Is 9.0c the XP equivalent of 10?
I use flight sims for recreation and would like the best performance out of them. I've held back from FSX mainly as it's a pointless upgrade over 2004 until I had the hardware to make use of it's features.