@xtcclassic:
My only concern with the IH t's I've tried is they are much too bulky and not really a "fitted" fit, especially in the sleeves. I'm fine with the 6.5oz part, although I'd be fine with lighter weight as well (I never thought I'd be all that interested in a 14oz denim from Iron Heart but I'm LOVING my new 14oz 666's). But to function as an undershirt, it should be more of a slim, fitted cut, especially in the sleeves.
Seconding this.
I'm aware that as a really skinny build, I'm in the minority of IH wearers, but this is a consistent issue I've had with looking at pretty much any IH shirting–I have slightly broad shoulders for my size, but otherwise need a pretty severe taper from the shoulders down to properly fit just about anything (only "shirting" I own is the IHTB-01 and even that needed a tuck-in from the pits down so I don't give off that shirt-mannequin appearance).
On the bright side, the shirting money can go towards another pair of jeans--it's all in how you view it, I guess.