FH,
You are correct, the manual does have a limit of 400gr on conicals for 150gr loads. I double checked with CVA about heavier bullets before getting the NE's and they told me for bullets upto and including the heaviest PowerBelt (which is over 500gr), that the max powder load was 100gr. I shoot them with 90gr and they shoot great. If the 400gr Whites do as well I may switch over though. Not neccessarily to push them harder but to flatten the trajectory just a bit.