I'm sure your method will work, but I don't think the Mr. Malty calculator is complicated. One of the inherent problems I see in your system is the cut-off points. You could brew a 1.050 beer and make a 1 qt starter, then another time brew a 1.052 beer with a 2 quart starter. That's a big difference in starter size for little difference in gravity.
Originally Posted by Stevorino
Where the calculator gets tricky is predicting the yeast viability - which is super important.
This is where, to me, his calculations lose their accuracy. Yeast viability is dependent on too many things to accurately quantify. His calculation makes assumptions about how the yeast was transported/stored (temp.) and probably even yeast strain, i.e., individual strains may have more "durability".
Undoubtedly, storage temperatures (including transport) are the most important. It's like milk. Most milk will not sour until a few days (sometimes up to a week) after the expiration date. If the milk was transported and stored in ideal conditions, the milk could last as long as 7 days after expiration date before souring. If the temperature fluctuated, the milk will sour quicker. It's a similar concept for yeast viability.
However, I don't mean to be too critical of his Jamil's calculator. He had to figure someway to quantify viability, so it's not a bad thing. I just think some of the starter volumes and numbers of vials of yeast should be taken with a grain of salt and they could be reduced if you think the yeast was stored well.