Aerocat has hit the nail on the head.
When doing a barrel roll in the PS2A I used to pull a consistant 3g throughout. The tighter the barrel becomes, the more g is required to maintain its shape. However less g will cause decreasing airspeed at the top point of the barrel, causing it to 'bottom out' severely. Remembering also the entry and exit altitudes of the barrel will be identical if coordinated.
The lesser g in the barrel can also be compensated by lengthening the barrel with a lesser roll rate.
The aileron roll as pictured above can be done correctly at 1g in most high performance aero aircraft, due to the requirement of only needing aileron to roll.
Either way, they can be both a hell of a lot of fun!!