Nik, I think there's a thread around here somewhere that talks about the mag length and maximum COL possible in a 300Wby Vanguard, but I haven't searched for it. I'll put in a call to a friend who owns one and see what he says. Might take a day or two to get around to it. The gist of it is that the Vanguard is on the long end of action lengths for both the long and short actions, and because of that, can accomodate chamberings that other actions cannot. Savage also enjoys this "longer" status in both action lengths. Compare that to Remington, whose long action is acceptably long, but whose short action is short enough to preclude significant seating length (COL) in various cartridges to prevent me from owning one. That's why the SAUM's are shorter overall than the WSM's - the Remmy short action won't feed the WSM's at full length!
The Mark V is clearly capable of H&H length, obviously. And for the price of a used Mark V (I've seen decent ones as low as $450!) one could easily have a $1200 custom 7mmSTW on a Mark V action, cerakoted in a nice satin grey or black, and then scope it out and have a heck of a long range rig, with the barrel contour/maker of your choice, and a decent aftermarket stock like the Medalist from B&C. Total cost would likely be something like $1800 with a good scope on it. Get nuts about the glass or the stock, and you could spend $4k and up on the project, though.