I'm doing this, did last years Whitehorse Challenge which was the shorter 75 miles, for me it's a local route,as many of the roads are included in our Sunday Club runs (NRC). There are going to be some interesting climbs, Ken Robson the VL Sponsor/organiser was the guest speaker at our Club dinner.
I haven't decided yet whether to go for a good time, or, to go for the just get round at my leisure .
Previous events have been well organised, and this years events should be even better.
The 200k ride will be my longest ride in one go so far, so it'll be a bit of a milestone for me.
My advice would be after setting off and establishing a tempo, try and attach your self to a group who are riding at your pace, and stay with them, sharing the load, take your turn at the front, riding in a through and off stylee, that way you will get round in a good time, and expend less energy, just make sure you have plenty of snacks and fluids, although there are water and food stops on the route.
If you do get dropped then don't worry, another group will come by, to which you can attach yourself. Alternatively get a buddy to enrol with you, and go round together.