When I was going on a cross-country trip on my F800GS, my dealer recommended Metzeler Tourances, and he said to keep them over 40psi to make them last close to 15K. I put one only in the back, I put a much cheaper Shinko in the front because I was sure it would last. The trip was 9,000 miles, no problems at all. I finally replaced the Tourance two weeks ago at 11,700 miles. The front Shinko still looked like it had about 3K left in it, so I put it aside. This turned out to be a great combination of value and durability.
2009 F800GS, 1995 R1100GS, 2013 Moto Guzzi Stelvio NTX, 2002 Triumph Tiger, 1984 Honda Magna with Velorex Sidecar, 1969 Jawa Sport