I have been on a quest to find the lowest possible base options for use with the 30mm tube scopes I have when using Burris Sig. ZEE medium rings. Here is what I have found...

This is my Vortex Viper 6.5-20x44 with Butler Creek flip ups sitting on my barreled action. It is a target action with a prefit Shilen barrel. The bases are Burris Extreme Tactical two piece #410615. This is the best combination I have found for this scope to get it as low as possible. I set my 6-24x50 4200 Tactical on top and it would NOT work, bases to low. For that combination I tried the EGW HD one piece rail and it worked very well. The Farrell one pc. rail works however it is about .10" taller then the EGW. With the Burris two pc. bases and a 50mm obj. scope you would need to go to high rings.
[img width=600 height=450]http://img.photobucket.com/albums/v318/Toobuilder/IMG_4076_1.jpg[/img]
[img width=600 height=450]http://img.photobucket.com/albums/v318/Toobuilder/IMG_4083_1.jpg[/img]
I also tried the Weaver #46S two piece bases. They are very similar in height to the Burris two pc. I much prefer the Burris two piece bases over the Weavers as the Weavers only have one cross slot compared to three on the Burris which allow much greater flexibility in mounting various scopes to get proper eye relief. I hope this helps with some mounting questions. TB