I am not a big fan of how Bathmate finds their perfect fit.
Instead of using BPEL to determine the length I would use BPFSL because the expanded size inside the cylinder is more close to BPFSL.
Additionally Bathmate doesn't make a difference between a ruler and the Bathmate measuring gauge. However the Bathmate gauge starts at zero, almost an inch away from the edge. The Bathmate tape will therefore give a different length than a conventional ruler.
Instead of using midshaft erect girth I would measure the largest girth which is often at the base.
At 6 inch midshaft girth one should easily be able to use a X30 Wide Boy, X40, X50, Hydro 9, Hydro 11 or Goliath. Looking at the chart in this thread the X40 would give room for 8 inches in girth. It is ridiculous to think that the second largest pump give room for already 8 inches. Nobody would be able to make proper use of the cylinders that are even larger. It is much more likely that the X40 is made for around 6 inches girth and that the X50 is then made for people above 6 inches in girth. There is no reason to believe that the market would provide 2 pumps that are made for people above 6 inches in girth because there is almost nobody that is above 6 inches anyway.
I have been using Goliath for a few years but I understand it is a bit too long. X45 Wide Boy might be a good fit for me. But we know it doesn't exist.