R/Upgrade Space to Europe

Hi,

I'm looking to travel to Europe on a flight booked in economy and upgrading to BF. Which of the following routes have the best chance of having open R space?

IAH-AMS
IAH-MUC
IAH-FRA
IAH-LHR
EWR-MUC
ORD-FRA

Any others that I'm missing?

Thanks!