A few weeks ago, I ordered the 15" (Large) Shinza sleeve that had been reccomended here on the NBF for the 3790. I got a response email from them saying...
Originally Posted by Shinza Sales
As is noted on the respective product pages, the 12-Inch and 15-Inch (Large)
models have recently been enhanced to provide even better protection against
impact shock. The new wire-frame exoskeleton and strengthened materials come at
the price of elasticity, which means that unlike its predecessors, these models
do not stretch to fit notebooks that are larger than the case's interior
dimensions. To ensure proper sizing, please be sure to measure your notebook and
compare to the interior dimensions listed below.
12-Inch Sleeve: 11.42 inches wide by 9.45 inches deep (290 x 240 mm)
15-Inch (Large) Sleeve: 14.0 inches wide by 11.8 inches deep (355 x 300 mm)
The dimensions listed do not match the dimensions of the 3790.
I searched around some more and found a laptop sleeve from Waterfield Designs.
The size 31 fits my 3790, with a 12-cell battery, perfectly. I hope that helps.