I would try cutters from Micro 100 or Harvey for top quality small cutter. Cut quailty has a lot to do with bits.
Joel, I do not have a vacum hold down system so I had to make do without it. I imagine if I had one it would have been easier to cut the brass.
Also I wanted to share a quick photo of the finished product. The sign pictured here is a sign made to go on the side of a boat named "Turkey Salad". Note I had a hard time getting a good photograph since it was requested to be black and brass with very high gloss.
The sign body is made of high density urethane (HDU) foam with 0.02" thick brass letters. The entire sign was then clear coated and polished to a high shine.