Yoshi-P has been demoed ARR on an Ultrabook running Win8 on nico-live event 2 weeks ago so it's no problem to run ARR on Win8.
But speaking for driver, a JP gamer's info site "4Gamer" tested FF14 benchmark (current version) on Win7 and Win8 for the same HW configuration, the Win8 loses some little (<100) score.
Remember, the driver issue can be solved very quickly.