I have an 800 yard range at my house.  I shoot each of these plenty from every position imaginable and they will all do their part at 800 yards.  Define "proficient"...I guess if I wanted to shoot a mile, I could be better, but for hunting the mountains I think I do fine.  Whether I buy a new one or not will have ZERO impact on the adventure hunting trips I already have planned (Kodiak for Brownies in the spring, Yukon for Dalls in the fall and Mexico for Deserts in the Winter.).  A guy only has so much time.  A shooting school has been on my radar for a long time and I feel I could benefit from one.  A guy can always learn.  AS far as selling 3 of them...I wish...For the money one pays for "custom", they hold no value accept to the guy who had it built.  If I was in to the "resale" of guns, I'd stick to production rifles. 
I am narrowing the field to 7mm WSM and 7mm 08 AI.  (and I haven't completely ruled out the .284)  I'll let Steve talk me into one or the other.  Keep voting...Love seeing the results.  Ton of .280 AI fans here.