I would wear a blazer and tie.
in my Pre-style forum days i was invited to attend a trip to vegas with the crew from the auto racing team i was working with.
One of the investors in the whole mess was a guy who was a serious steak lover, so we went to Charlie Palmer's in the four seasons.....in t-shirts, jeans, and me in a pair of work boots.
I think we offended everyone's sensibility quite thoroughly, the owner's best friend's Uncle was a chef there at the time, and declined to come out and say hello to us.
I dont think the manager minded much though, everyone at the table ordered ordered lobster and double orders of Kobe steak, and the best part. The waiter graciously asked us if we would like to know what the market price was for the steaks we were ordering (none of us had any idea the price of kobe) and my friend Adam looked at him and say...."nah, we're not worried about it".
Later on, after they sent us round after round of appetizers on the house, we found out the steaks we ordered were $200/ea and the bill for 6 people totaled $1600.