Eh, didn't mean to ruffle your feathers there buddy (although I should have expected somebody would react). Just sharing my perspective, wasn't addressing you personally at all.
I'm not speaking from total inexperience - at around 5.5" midshaft I never felt constriction, even towards the bottom half which is thicker. I've also put a condom on after some fairly intense clamping where I was pumped up to well over six and didn't feel like it was particualrly painful/difficult, it actually felt fine, seemed like I could easily maintain an erection. Just my experience though. We bought a pack of XXL rubbers as a gag gift for a notoriously average endowed guy one time for his birthday - and the look I got wasn't flirtatious, it was more like pity. Glad I don't feel compelled to buy those things regularly.
I think the width of the Magnums is supposed to be around 2.2" unstretched - that seems wide enough to accomodate a pretty large penile width already. The big boy XL ones are over 2.5" width, unstretched. That's pretty freakin' huge for a standard erection. I think a normal condom is about 1.65" wide - meaning it gets stretched about a half inch on an average width dick. That means even the Magnums aren't stretching much at all on most guys as not many can boast a width approaching 3", I think.
The big ones are also around 8" long unrolled. I think the average ones are a little over 7" - and frankly I haven't seen too many guys on this site that could max either of those stats out. Due to the nature of latex, most condoms will stay on your cock even if not at optimal tightness, they make sure of that. Hence the 15% of the market that uses them but doesn't really need 'em . . . not saying that's you or anything, but that's definately a part of their market share. Could be a little off on the size figures, they're from some men's health website, but I think they're pretty close.
Like I said, I just always felt like it was a bit of a piss when all these guys I knew were griping and moaning about how terribly constricting normal condoms were, especially now that I've read that only like 2% of men actually really need a bigger one, and I've had at least one experience where a girl I was in bed with mocked a previous encounter for triumphantly producing his magnum condoms for a penis that really didn't need them. If I ever have to go back down the condom road, I'll be sticking to the regulars, even if I manage to develop a really large girth (6+ at least for an average wood).