UA starts flying to T2 at LHR on 6/4/14.

We have a flight in mid June from SFO-LHR arriving at 7:10am at T2.

I'm trying to book a separate ticket for onward travel to CPH on either BA (9:55am) at T5 or SK (12:25p) from T3.

As neither are located in T2 - I'll need to transfer via bus (T5 vs T3)

I assume 2hr 45min is more than enough time to catch the BA flight and save myself waiting another 1:30h in the airport for the SK.

Will UA have any problems interlining bags when I check in at SFO through LHR to CPH if these are separate tickets? Or is it better to catch the later flight to stay in *A. The miles don't matter that much to me as it is such a short flight.