I used nothing but mechanicals up until this year. But I found that I simply cannot pull the poundage required to achieve the proper kinetic energy (55 pounds of KE was all I could handle...old shoulder injury).
I switched to Muzzy's this year and my groups only opened up slightly.
I was not impressed with the penetration of the mechanicals, although, as I said, my KE was on the bottom end of the recommended spectrum.
I killed 6 deer with the Muzzy's this year. All but one was a complete pass-through. The other was low and forward a bit, and completely blasted a hole through the upper leg bone, and then into the lower lungs and heart area (shooter error)...the deer still died within minutes after going about 80 yards.
I love the penetration of the Muzzys but I also love the tighter groups of the mechanical stuff.
Are the Snypers achieving "pass-throughs" with lower kinetic energy?

"Soon the entire place is alive, and sitting motionless, you realize that you have been placed in the center of its pulsating heart." - From an article by Carpicon at Huntcentral.com