What I would reccommend would be to not be set on a certain length, but cut to tune. If the numbers in your original post are good (and they do seem to be in the realm of what should work), you could leave that shaft 1/4" or 1/2" longer and be tuned near perfect.
Also, if you are using a claculator like Stu Millers or 3Rivers, that has a Personal Form Factor (PFF), unless you are one of the lucky ones who ends up with a "0" PFF, the calculator will be off (that can range from slightly to waaaaay off) unless you have a known well-tuned arrow to enter and get the PFF set for you.
The only constant I have when I tune is point weight. This is because I have a good amount of $$$ tied up in my German Kinetic broadheads, and those are what I am going to use. Every other factor is variable to me till I get a great tune. Once my arrows are tuned good, the critters better watch out!!!
Good luck getting things right.
Bisch