I use 13x19 paper to print anything and everything I print larger than 8x10. I use primary Epson Velvet and UltraSmooth Fine Art papers and it's just easier to order in two sizes (8.5x11 and 13x19). I
always leave a margin on these and size the print to be just larger than the mat size, so if I wanted a 13x19 print I'd actually print it to a mat cut size of 12.5 x 18.5 leaving 1/4" of print covered at each edge.
I had a website bookmarked that had a mat and frame size calculator that would give you the common mat sizes that work for various print sizes, but I seem to have lost or deleted it. When I come up with it I'll link it here (I suspect I've linked it elsewhere in the Printer section if you want to search).
I too have a Logan mat cutter, but have used it more for cutting foam core backings than actual mats since most of my prints are standard sizes. It's a great cutter, but they're not cheap and you want to make sure you'll be cutting enough to justify paying for one. I've found the precut stuff I can find at Michael's works for 95% of what I do, and they'll cut mats for you for a cost (not sure what it is) so unless you plan on doing a lot I'd look into local places that will custom cut mats for you first and see how many you need to do before justifying the expense of the Logan (which needs to include the mistakes on the first X number of mats you try

).