Also, apparently Intel is planning to extend x86_64 to 32 GPRs, with an extension called... sigh[0]... Intel APX[1]. So the overhead of frame pointers will be even lower in the future.
[0] Intel APX is extremely confusable with the iAPX 432, a failed non-x86 architecture Intel made that's completely unrelated to doubling the size of the x64 register file.
