Best upgrade chances SFO - Europe in Early October

Hey all,

I'm looking to buy a flight from SFO to AMS in early October using a GPU to upgrade. I need to leave at night, so most east coast connections are out of the picture. As of now, my options look like this:

UA SFO-FRA-AMS (744)
UA SFO-LHR-AMS (744)
LH SFO-FRA-AMS (380)
LH SFO-MUC-AMS (A340)

As of now, there is no R space available on the UA flights. So, I'm debating the following:

1. Waiting to purchase until R opens up on either the FRA or LHR flight. (probably unlikely)
2. Picking one of the UA flights that R is most likely going to open up on (I'm leaning FRA since there are double daily UA 744s and a LH A380 on that route, so lots of capacity)
3. Buying a flight on LH and hoping to score an upgrade at check-in.

Any insight on preferred strategy? How do loads on the evening UA departure to FRA/LHR normally look, and what's the LH upgrade chances on those flights? I'd prefer to stick to UA for the lifetime miles and for the flat-beds but the ultimate objective for me is to be in business and not the back of the bus.