How much difference is required for you to take notice or find it meaningful? As clarification, Surly claims the chainstay length is 460mm on all LHT frame sizes. Grand Tour varies from 430 to 460, difference of 30 to 0 between the two frame models. Not sure where you identified the 5mm difference.

http://surlybikes.com/frames/trucker_deluxe_frame/
http://surlybikes.com/frames/long_haul_trucker_frame/
http://gunnarbikes.com/site/bikes/grand-tour/

What criteria are you using to claim one make is good and the other make is very good, or this just an opinion?