James,

I totally concur with Kokonutz. Those am flights to LHR are a lifesaver! AA offers 2 out of JFK, 1 out of BOS, and 1 out ORD, and we always try to fly one of those when we go to Europe. Yes, it makes the itinerary more complicated (it means continuing the next day on BA from LHR to BLQ, MAD, AMS, ARN wherever we may be going at the time), more expensive (often two tickets), and more time-consuming (one extra night in a hotel at LHR for us), but what a huge difference when we get to Europe! Then, if an international upgrade is not available, it's not the end of the world: a seven hour day flight in coach is not ideal, but it doesn't begin to compare with the ordeal of 9 hours on a redeye in coach (especially in summer when those flight are regularly full).
Unfortunately, I believe that LHR is the only European destination that can be reached by flying during the daytime (except, of course, Concorde flights to Paris, enough said). I've no idea why daytime flights from the East Coast aren't offered to other "near" European destinations such as CDG or AMS. I can sort of see why JFK-FCO wouldn't be very practical (getting into Rome very late at night), but CDG and AMS are only a few miles farther than LHR... I will miss BA's connections from LHR if they end up leaving 1world

Anyway, to get back to the thread topic: I would definitely upgrade on the Europe-bound flight. A good night sleep is invaluable, and helps keeping jetlag in check. The Westbound flight is slightly longer, but when you arrive, you can just have a good night rest.