Anyone have any experience with Vortex Optics? I was looking at the Viper 6.5-20 or Viper HS 6-24. They seem to have pretty good pricing, but I was not sure how they stacked up to say the Leupold VX3 6.5-20. I will be using it on a 7mm Rem Mag that will double for mule deer hunting and long range target shooting (for fun, not competitively), long range being 300-600 yards.