Stepsisters have a cranking contest (Zoey Holloway - Raylene) taboo handjob

My step-sister and I have always been competitive with each other. We've nabbed boyfriends from one another and even fooled around with each other's boyfriends and husbands on occasion. I told her about the day I jacked off my step-son in my bathroom and then brought him over to her house to get in on the house fun. Not to be outdone, she immediately started her own perverted routine with her step-son. We are having a casual conversation one day about our new found bond with our step-sons when I could feel the competitive nature between us brewing. When I mention I think we should have a contest, she of course replies that she will win. This statement just fuels my fire to definitely have a contest with her of who can jack off their step-son to cum first. The loser has to treat the winner to a day at the spa. How can I fight that offer? I've been wanking my step-son the longest so naturally I should be able to bring him to an orgasm the quickest.