Looking for a recommendation between either the Thorntail SBR or standard Thorntail light mount.  I want to replace the Magpul light mount that I have currently with one of these two mounts and I want my light in roughly the same place.  The light is a Streamlight Polytac.  

Here is a pic of how it's currently set up.

Thanks!

THORNTAIL SBR. Would place the light and tail cap in the same position as your current set-up. The THORNTAIL would place it 1" further forward.