Why get the 7740X? That CPU makes almost no sense as it has nil resale value and disables tons of features on X299 motherboards. Unless you are absolutely certain that you will get a higher-end model in the not-so-distant future, it makes no sense. And if you do plan to upgrade the CPU, you may be better off eating the $200-500 extra up-front instead of burning $350 now and another $700+ later.
To make things worse, there have been rumors that the 12-18 core models may require a new socket revision, which means LGA2066 could be a dead socket by this time next year.