I find that padding is a trade off between benefit and painfulness. For me, SFO-LHR becoming SFO-LAX-LHR is a good bit of padding and relatively painless. The domestic sector, which is the very painful one, is short and earns 500 mile minimum (ie more than you actually fly). Plus, adding 100 + miles to the TATL sector helps. Whereas SFO-IAH-LHR is very inconvenient for me, with a long domestic sector and worse flight timings for not that many more miles.

Plus, remember that, after March 1, you will still earn PQMs the old fashioned way.