I think at White Rock you would merge with half marathoners in the 1:25-1:30 range moving considerably slower than you'll be moving. There is a one hour difference between the marathon and HM start. Last year I ran around 3:10, but I started way too slow and so was running about 6:40s in the last few miles. Ran right into a bunch of 10:00+ HMers jogging/walking 3 or 4 abreast, chatting, and iPoding. It necessitated weaving, curb hopping, near collisions, and anguish. You, however, might come up on a more sparsely populated group of runners and not have to move around any. White Rock is a little hilly, but the finish is fast, the weather is good, and the crowds are nice.