Three of us used various combinations of Nashbar or Performance panniers and I used the handlebar bag you mention for the TransAmerica. Each of us had two Nashbar Waterproof Panniers, some the larger rear ones and some the smaller front ones.

Everything held up fine and we found them all quite satisfactory. A couple of the little Velcro tabs tore off of the panniers, but the panniers stayed on fine until we got around to sewing them back on.

Gear stayed quite dry in the panniers.

When the panniers are off the bike be careful not to lose the metal hooks on the bungee retainer system. We almost lost one a couple times when we had them off the bike.

My handlebar bag was pretty overloaded and there were rough roads a good bit of the time. As a result it did sag a bit during the 73 days on the road. It was never a real problem though and I beefed up the stiffening stuff inside after the trip (fairly easy to do). The waterproof zipper is pretty stiff at first, but loosens up over time. The bag is pretty waterproof, but when it REALLY rained I put a plastic grocery bag over it just to be sure since it had my electronics in it.

All in all... I would buy the same stuff again.