Going on a new 20" build for precise target shooting and varmint hunting 100 to 400 yard

Price range around 600 and I already have a LT104x30mm mount

I am looking at the following choices:

Vortex Viper PST 2.5-10x44

Leupold VX-R Patrol 3-9x40

Any opinions or reviews?  Also, Is there any other optics I should look at?

Define "precise target shooting" please.  I have the 3-9x40 VX-R Patrol on my lightweight hunter bolt rifle.  The optic is great for it's intended use (Whitetails out to 400 yards), but the reticle is a little on the thick side for trying to shoot bughole groups (if that is what you're after).  I love the illumination control/motion sensor and the glass is surprisingly good for present-day Leupold.  Overall, it's a great little optic.  Gonna pick up the 2-7 VX-R for my lightweight coyote AR.  

Can't comment on the 2.5-10 PST as I haven't shot with one.  I do have a couple of the FFP 4-16 PST's and like them.  Since the 2.5-10 is not FFP, I would assume that the reticle would be a little thinner than it's FFP cousins.