The D-300 is a great scope built like a tank, BUT the prices keep going up and up on these units do to the VERY limited availability of the US Surplus Gen 2 tube. With that said the GT-14 in a Gen 2 SHP B Grade (Super High Performance) is a GREAT tube with the closest resolution to a Gen 3 tube (57-59LP typically). Mil-Spec Gen 2 US Surplus at 29LP. Presently the GT-14's are just about the same price as a D-300 Gen 2 unit at $1600. Hope this helps and happy to be on this forum!! I've been a LONG TIME 6.8 user.
Vic