I got a Grape drop doing patrols the other day. And I've received two Grape engram rewards at the end of Tiger strikes, in addition to the consistent blues. But I've never had a Grape pop out of an enemy during the strike. Just lots of greens, and the occasional blue. Personally, I'd rather go fast and hope for good rewards, since you are guaranteed to get them, whether they turn out great or not. For me, a Guarantee trumps Chance. I do however wait for the other Guardians if they are slower, and I even turn around to shoot enemies if they're having trouble getting through the unnecessary spots. They usually realize after seeing me go quicker that you don't have to bother with the trash, and then I see them getting on their speeders to go quickly to the next part. I'm glad to have educated them on how to efficiently do strikes, lol.