Having sailed out of Milwaukee for 7 years I would say go 150 or 155. You can always reef down, you can't reef up. Unless you are into serious racing I would not worry about high tech sails. BTW I don't think there is enough serious competition in Milwaukee to warrant spending more money. I also suggest that you get in touch with MAST - there are a number of 27's in the fleet and they are nice people. Link to their website MAST Racing - Welcome
They are very nice people and do low key racing on Friday nights. Several members also do the Hook and the Chi-Mac on a regular basis.