Currently I cashed in some US Airways miles for two Envoy (business class I guess since US Airways doesn't have 3 classes) tickets on US Airways this winter (early Dec). They cost me 95K miles each (5K discount since I had a US Airways CC). The international leg is PHL-CDG.

I'm not as familiar with United miles since I've cashed in most of mine.

US Airways does have off peak Envoy awards to some European cities (CDG is one) during parts of Jan/Feb and are 60K miles (with the CC they can run 55K miles) per ticket R/T. I might be wrong on this but I don't think you can use United miles to get the off peak awards.