Is anybody using an improved Ultra mag or Lapua case?

I'm getting started on building a 375 "something" to shoot the Sierra 350gr Match Kings. I have it narrowed down to either the Ultra Mag case, or the Lapua case. I have some 375 RUM brass sitting here and I loaded up a dummy with the 350gr MK for inspiration.
[img width=600 height=450]http://i162.photobucket.com/albums/t260/collegekidandy/375ultra.jpg[/img]
In the picture from left to right: 6mm BR 105gr A-Max, 300 WSM 185gr Berger VLD, 338/375 Ruger 250gr MK, and the 375 RUM 350gr MK.

Now I'm just trying to decide if I want to use the straight 375 RUM, an improved version of the RUM, or use the Lapua case instead. From what I can tell, the RUM and Lapua cases have similar capacities. The RUM brass is less expensive, but the Lapua has better quality brass available. I'm leaning towards the RUM just so that I don't need to worry about the larger Lapua bolt face. What does everybody think?

Andrew

No point in "improving" the RUM case. It already has almost negligible case taper and a fairly sharp shoulder.