With the increase of fuel prices premium still remains $0.20 - $0.25 more than regular. Interestingly at $2.00/gallon the same was true.
So currently its about 5% more for premium fuel than regular. Check your MPG closely as it may drop that much. Mine definitely does drop that much in my premium required car and the power loss in noticable. However the motor (Subaru WRX) is more a sling shot powerband than a flatter one like a BMW.
Check your MPG over a full tank with regular.