Boost clocks are rarely the actual clocks of the GPU anymore. The base and boost clocks you see advertised are the minimums the card should run at, but GPU Boost (NVidia driver technology) will also overclock every GPU that GPU boost determines can be overclocked further. Sometimes that is substantial, sometimes it is minimal.

The base and boost clocks advertised by all of the manufacturers, to include NVidia’s own cards, are probably not going to be what the cards actually do at stock, the cards will probably run somewhere around 1850mhz or higher on their own, so your card is already overclocked from the factory, on top of what the manufacturers are also displaying.

A card with a factory 1710mhz boost can still match the clocks of another factory card with a 1755mhz with GPU Boost alone, without any end user overclocking at all. Sadly, there is no way to turn GPU boost off, so in the end, you are paying more to guarantee higher clocks if the card runs into a constraint like power or thermals.

The cost difference is guarantees that the card will run around that higher boost clock, as long as all of the environmental aspects are kept under control.

The founders Edition, XC3, and FTW3 all use completely different PCB’s, so that will be another, non overclocking, limiting factor.