Re: Tomahawk (300 RUM imp.) vs WarBird???
I think the Ultra Imp and the Laz offer minimal gain. If you're going to do it, might as well end up with top notch brass and go Lapua.
I do get a decent gain over the Ultra, and seemingly with less powder in my 30/338 Lapua Imp.
I think the largest gain was with the 178gr AMax, 3500 fps in the 30.5" bbl. I took it to 3650 but it was pretty damn hot!
About 3200-3250 with the 210gr bullets using RL25 and Retumbo. Those loads are a little hot, up around 70,000 psi, so you'd get about 50-75 fps less if you dropped to around 65k psi. Still, slightly better than the Ultra, but it does have a 30.5" barrel over my 26" factory tubed Ultra though...
Like Jake said, I'd go with the Ultra if you weren't going to do the Lapua, it's no slouch!