
CJC,
I'm also 6'5" (although I have relatively short legs or a long back). I can't say I've ever tried the ones you've suggested although my first sack was a Karrimor (from way back yonder).
Firstly I'd suggest you don't buy a sack without trying it- but I guess you already know that.
I had to shop around a lot to find a sack that fitted me. From the looks of it I'm guessing you want a really big one- I did consider the ones you mentioned but couldn't find any and that for me ruled them out.
However ones I'd try would be Osprey Crescent (really comfortable but maybe too many features- but its the one I went for- large harness size of course), MacPac Glissade (probably would have got it but couldn't get harness size four and three was too small). Lowe alpine harnesses were also large enough but the sack was more basic than I wanted (I seem to recall). I'd love to hav got one of the Arc'teryx Boras but there weren't many in the country at the time and I'd have had to have sold a kidney.
That's some of my experience from having gone through the same process- hope its useful although it doesn't answer your question- but I'd think long and hard about buying blind for a big rucksack