Your file is shaping up rather nicely. It's a little difficult to come up with criticism, but I think I found one:
I don't like your SIZ results. They're a little wonky if you ask me. A Hill Giant has a SIZ range of 10 to 40, with an average height of 25?
A midget Hill Giant is the same size as an average adult. That's kind of funny actually.
I think you should flatten the curve just a little. I see from your formula, that you are expressing SIZ directly from STR. I wonder if you subtracted the size bonuses from the Characteristics before you computed their BRP equivalent? A Large creature, IIRC, gets a +4 Bonus to STR, and a -2 Penalty to DEX.
In any case, SIZ is probably the most difficult Characteristic to convert formulaically, but like I said before, it looks like it is really coming together.