For me I have a budget and try to stick to it unless there is something about price to performance that dominates enough to make me spend a little more.
Thanks to brandonmatic with the poll.
It would also be interesting to see how people's poll choices match what they did in their last GPU upgrade. I chose same price for 50% more performance. My last upgrade was from a 5850 to a 7950.
I want at least 50% more performance for the same price as my current GPU. I actually upgraded yesterday, after four years with the same GPU. I upgraded from a HD5870 1GB to an R9 280X. I paid 30% less for this new card and the performance is 70-100% better. I'm quite satisfied.
It's also quite amazing how well the i7-860 is holding up after four years (overclocked to 3.6GHz, though).