When I flew from SFO last October, I used a J open jaw SFO-LHR-KEF LHR-SFO, then bought a separate nested leg from KEF-LHR and spent extra time in London. This meant the critical connection was protected and I had the option for economy on the KEF-LHR leg to keep costs down. And being October, I also read up on all the nifty road condition and weather tools available in Iceland. I was able to navigate the winter weather without running off the road like 24 others did on the last two days.