I have a vortex viper pst 2.5-10x32 ffp on my Scorpyd crossbow, and a Vortex Razor HD 1-4x24 on my other Scorpyd crossbow. I love both of them. They both were built with AR platforms in mind and really are a lot of scope for a crossbow, but I like good knives and I like good optics.

[Linked Image from farm3.staticflickr.com]