Very interesting. I always use the 1800fps 'golden rule' too and have built my 300 rum loads around that notion. Just for safety's sake, I'll probably continue to use the 1800fps rule since I've already got an 880 yd (where it drops below 1800fps) load built w/ the 200g LRX (formerly the TTSX).
Following Barnes' comments, however, that would make my load a 1000+ yd load. According to JBM, my current load is still moving at 1636 @ 1000yds.