In the next year or so I plan on building a fast 7mm. I started out wanting a .280 AI, but now I'm thinking about just doing the 7mm mag due to brass availability, price, and a little bit extra speed. Now I'm wondering if I should just go all out with a 7mm STW or 7mm RUM. Is the extra velocity worth the price? Most of my shots will be under 600 yards. BTW, I already load for the 7mm RM for my dad, so if I went that route, I wouldn't have to purchase a die and accessories. Also, I already have a donor rifle in .30-06 in a Rem 700 (blued action from the early 80's). Do either the STW or RUM need a longer action? I know the bolt will need to be opened up, but other than that, what modifications will need to be made?