Re: lazzeroni cases
Not to confuse you, without knowing your longrange experience and going from what is in your post I'd say first that being pulled in only two directions (Laz or RUM) just isn't enough. At least 3 or more directions would be more fun. Hey, if you're in the dream stage why not dream big!
Next I'd agree w/Goodgrouper.
Finally I'd throw another cartridge(s) into the decision making. These cartridges have all of the coolness to strut around the range with just a touch of arrogance, incorporated into one of the cartridge designer's rifles (you mentioned building) and with the bullet for which the cartridge is designed (169-195 or 200gr ULD), the ability for deer, out towards 1500 yds.
Put the 270 or 277 or 7MM Allen Magnums into your cartridge consideration and evaluate them against the Laz or RUM (7 or 300) and you will be pleasantly surprised.
Just my tho'ts, hope this helps....
I'm sure you'll enjoy the results of which ever cartridge and rifle you select.
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!