If you are wondering how your time will stack up to a 1/2 marathon road race (and wondering if you will finish under 3 hours) then you can use this rule of thumb: Add 15 minutes to your expected road race time to guesstimate your finishing time here.
The trails vary in their complexity, with the Leatherstocking likely adding 2 min/mile to your regular time. Other trails have a few wide flat stretches that can move you almost to road pace. Not many, mind you, but they exist.
The 15 minute rule is based not only on my years running these trails, but on a comparison last year of people who ran both P2P and the Westchester Half the following week.