Self-employed and my T&C's say over 6 hours is business class. However, there's always a degree of flexibility. Went to China for a smallish business and travelled in Economy (BA - not bad). Am currently working at a FTSE 50 subsidiary in California, and business class wasn't an issue.
The nature of my work means I know several weeks in advance that I'll be in x Location for a set number of days or weeks so I will book a restrictive and cheaper ticket. (I got MAN-AMS-MSP-SMF in business for <£2400 all in, when BA wanted over £6k). I will also be flexible on routings if that has a significant impact on price.
I once got a cheap F ORD-LHR for less than the client paid for J, but I wouldn't typically fly real F (non-US domestic) if a client was paying.