@dlearl476- Yeah, those cans are really cool; do you know anything about either oil's formulation?
Miller more so than the Castrol. I spent about a 45 minutes talking to someone at Miller's US distributor. (Performance Racing Oils) Both are made with increased ZDDP and anti-corrosives, but with modern lubrication base stock formulations. I called because I wanted to hear their spiel about mineral (Pistoneeze) semi-synth (Classic Sport) and full synth (Classic Sport High Performance). I spent about 45 minutes talking to their tech guy and decided on Classic Sport 20W/50.
Here's the specific page for the semi-synth Classic Sport.
ps: I just noticed on their website when I went to grab that link that they're stocking Millers GL-4 80W/90 gear lube now, too. I'll post a review when I get a few miles on the engine oil. I'm sticking with Motul Gearbox (mineral80W/90) gear lube for now.