I've been saying this all of the years I've been into computers and trust me there have been many. 35 at last count.
When it comes to buying computer gear always spend the absolute most you can afford to spend. It's far cheaper and more sensible in the long run to save up and buy the best you can afford because it will stop you spending more money in the long run on upgrades to keep you in the loop.
For example. Greg bought two Titans at launch. He then got to sit back whilst Nvidia released, and probably isn't limited to -
GTX 780, GTX 780ti, GTX Titan Black, GTX 970, GTX 980 and anything AMD made during that time.
I've actually witnessed people first hand going through most of those yet skipping the Titan. Yet, had they bought a Titan they would still have it now and only really now would they have a viable excuse to even think about replacing them.
Now of course, YMMV, but at the end of the day if you class yourself as an enthusiast it's far cheaper in the long run to buy the best as it buys you a far bigger "don't need to upgrade" window.
I'm not happy about what Nvidia charge for Titan but as much as I hate the price there's no denying their prowess when they're released.