When you increase case size, all other things staying the same, you can expect an increase in velosity of 1/2 of the increace in percentage of case capisity. What that means is when you get into larger cartridges it takes alot more powder to get a smaller increase in velosity. That plus you will get aprox. 5 more yrds of max. point blank range for each increase of 100 fps. With the large volumes of powder burned and the fact your shortening the barrel life with the hotter loads it becomes a matter of is the small advantage worth the extra cost.
I personally believe that that the BC of the bullet is alot more important in long range accuract than is it`s velosity.