I'd spent the last two years trying to find a pack that would fit me in that 45-50L size - finally discovered that all of the internal frame packs I was trying had the same issue of the load lifters making a zero-degree angle, and I couldn't take the load off my shoulders. (I could avoid the neck-pull issue by keeping the load lifters tightened all the way.)

Finally, some one noticed that the problem wasn't getting the shoulder strap length right (20-plus, but not quite 21, inches.) The problem was that the actual frame length of the pack was too short, so the load lifters wouldn't attach higher than the shoulder straps. He recommended the Atmos 50, and it was perfect. If you haven't tried the current-year version of the Atmos, do so - it no longer has a fixed-length shoulder strap; they changed to an adjustable-length harness this year. (The fixed-length never fit me right: medium was too short, large was too long.) It took a bit of fiddling to get the adjustment just right, but it was worth it.

So, if you haven't tried the adjustable-harness version of the Atmos, give it a look.