Don't do it. Too short. Remember you do not sleep flat footed and also need room for loft at both ends.
I am 6'6" and I suffered through with 80-84 inch bags for years. (yes 84" bag is too short for my 78" frame) My current bag is in the 90 inch range and this past year was awesome. It had been over 20 years since the last time I could Comfortably sleep with the zipper all the way closed.
Go longer. I know most long bags are still to short, but there has to be some out there. The bag I am using now is an old model EXTRA long Moonstone bag from the early 1990's with Polarguard filling. Love the bag (it was my Dad's, hardly used and stored good.)
If you are spending money on a pricey bag, go longer. A good expensive bag is worthless if it doesn't fit.
Good luck.