Um...no problems here.

You're familiar with the road (and if you're not, become one with it...in the metaphysical sense only). It's 1.5 miles dropping 800 feet with four swooping turns as you drop into the valley.

Physics tends to say that objects moving in straight lines tend to stay that way. Worst problem I've had on on a bike is shimmey, usually caused by poorly distributed weight. On Oakville, the issues are ratty pavement (it's pretty good in general, though there's a couple of rough spots), oncoming traffic, wildlife, and your hardware flying apart on you. Plenty to focus on at that speed, but keeping the bike upright really isn't the issue. More than enough angular momentum to see to that.

As for for standing in the pedals, amazingly enough, my weight distributes pretty evenly across the pedals. No need for a lock-out. And if I need motive power, all I've got to do is start spinning.