About the first month of NAT RVSM in '97, I, in a loaded C-5, was approaching landfall in Gander airspace, when an opposite direction B747 (FDX, IIRC) passed a 1,000' above. A minute later, after a brief discussion along the lines of "what's this gonna be like" we hit the wake--rolled 30-40 degrees, autopilot said, "I can't do this, about you guys try it". Ever since, especially flying bizjets, even large ones, I've been cautious around heavies