I also have issues with arm room in sleeping bags, I sleep on my side and like to have my bottom arm out in front of me with my forearm pointing straight up towards the top of my head.
I have two Snugpak Softies and I've found that if I don't pull the face and shoulder baffle cord too tight, I can fit my hand up between the gap in the shoulder baffle and up into the hood. I used to have a center zip bag and it used to drive me nuts trying, (in vain) to find a comfy position for my arms. Get one with the zip on the same side that you're most comfortable sleeping on, this works pretty well for me.
They are good and warm and really well made, my only issue with them is that the zips tend to snag a lot.