Jacob,
You should consider the T&T line rating as the highest line number of the common 2 wt spey line designation. In other words, the T&T 1510 should be considered to be a 9/10 rod, while the Loomis GLX or Loop are 10/11 rods. If you want a 10/11 rod from T&T, you need to get either the 1511 or the 1611.
All the T&T 2-handers are rated this same way. For example: the T&T 1409 is an 8/9 rod, the 1307 is a 6/7 rod, etc.