What do I lose putting a 3.0 card in a 2.0 slot? Is it that there aren't any PCs available with 3.0 slots at a reasonable price?
You would need a high-end motherboard from Intel or the lastest Saberooth TUF series for AMD CPU's in order to get the 3.0 PCIE lanes. Now, you would lose nothing at all when putting GPUs into 2.0 PCIE lanes. It's still x16 and that's what matters, you're getting full performance out of your GPU.