Budget - ah yes that is the thing - unfortunately I like all most probably want Porsche but only have Proton money.
I don't have a defined budget but what I will say is that I (and probably everyone else on the forum) want the absolute best value for my £'s. I have thought about the used option and have been looking around getting an idea of prices. Although the down side is that you just don't know what sort of use the bike has been put through so there is I suppose an element of risk. With the new option you should at least get some form of warranty. From my perspective I think best value would be NOS or un ridden ex demo.
With the self build option I can spread the cost of the build over a number of months so it won't be a big hit in the wallet at one go and this allows me to seek out the very best prices and spec that I would like based on what I have read and reviews etc. Although that said I know that most of the big retailers do offer credit lines which can help.
Where I will ride, I know is an important factor, initially it won't be down the side of Ben Nevis! I will want to learn to ride properly (I know how different off road riding is to my present experience) - I very much appreciate that there is no point in having a £4K bike that I can't ride properly and end up being so frustrated I end up selling it as a result. I will start buy riding around my local country park (allows riding) to build up the fundimentals and my LBS are looking to start a sunday club for all levels and then as I improve I will look to graduate onto more technical and lumpy stuff.
Once the trade is learnt (although you never stop improving) I want to look further than my rather flat back yard - Lake District, Scotland, etc and travel abroad as well. Also I will be emigrating to Malta and that is fairly rugged terrain (just a limestone lump in the middle of the med) and will hopefully getting to the Dolomites with the wife (she'll be working with her job while I bugger of riding).
Perhaps I have got too much of an eye on the future rather than the now, again all reasons for making the post to the forum, making me think rather than making an expensive rash decesion that I will regret