A few hints from someone who abuses RTW's in the US, for BA status.
DFW/ORD - SJU is a winner. The best year-round route to pick up 120 points (as the flight is over 2000 miles).
MIA - LAX/SFO is the best transcon route as you have a good chance of getting a 767-300, plus they are 2 class, allowing you to book in A and earn 180 points.
If you choose to fly YYZ - LHR, why not try YYZ - ORD - LAX - LHR, which earns a cool 220 points.