When I bought my wife her engagement ring I wanted to put it on Amex but knew I should probably call ahead. This was quite a princely sum.
I called PCS and was on hold for about 10 minutes after which I spoke to someone who clearly didn't do too well in maths at school. I got so fed up I called Diners Club (the old BA Executive Club DC) who approved within about 15 seconds.
I walked out of Tiffany's with some heart palpitations but one hell of a lot of miles!