In my situation, it is probably best to aim for instructing for at least half a year as, at least, I'll have an income and gain hours (its just that I absolutely stink at teaching)
Stanziel, if you absolutely stink at teaching then I do not recommend you become a flying instructor just to build your hours for a few months before moving onto an airline. I would also be careful about saying things like that on this forum. Us 'hour-building' instructors have enough unpleasantness and negativity to deal with from some of the career instructors, and find it hard to convince them that we are actually decent instructors. The attitude that you are taking towards instruction, ie, that it is very much a means to an end, does not do us any favours and just give them more ammunition.
From a practical point of view, if you are unable to afford both, then go for the IR. If you get an FI rating then work as an instructor I can almost guarantee you will not be able to save money towards the IR. I can barely afford food and petrol on my FI salary! I don't know where the figure £10000 in 6 months came from - I find that highly unrealistic.
TB