Here is a quick link to a guy's review of some lighter weight reels, including the CFO and the Battenkill (Large Arbor - not the Bar Stock):
Three and Four Weight Fly Reels - GearReview.com
He weighed each reel (the second weight value). For some of the reels, there is a noticeable difference between specification weight and his actual recorded weight. In his review, he mentions that he had a tough time identifying around a 1 oz. weight difference.
I would tend to agree with that statement when you're comparing off the rod, but it might be different (not sure) on how it would affect rod balance and perceived weight when casting.
FWIW, the weight difference from reel to reel may be similar to stereo shopping. You may notice a difference at the store when you have multiple systems lined up in front of you in a room designed for auditioning, but you won't have that environment when you bring the system home.
If you have a chance to mount them and cast, I'd say go for it. If not, I would probably prioritize other factors such as build quality, warranty, price point, aesthetics, etc.