Flare,
I use all the above in the 6mmBR Norma and .223Rem. I tend to reach for the CCI450's a bit more than the others, then BR4's, Rem 7.5's and CCI400's last. All have produced sub 1/4" groups for me in the two cartridges listed.
I have a few of the Rem 6.5's but rarely use them. Too much controversy dealing with those. Some folks say "use 'em", some say "don't". I think they were developed for use in low pressure rounds like the 22 Hornet but I have used them successfully in the .223Rem with good results.