Share 'Sizing question - Felt f35x'

I just ordered a Felt f35x and had a sizing question. I am 5'9" with a 30" inseam. The fitter recommended a 51" frame. This seems a bit small. Any thought would be greatly appreciated. The bike's geometry can be found here - http://www.feltracing.com/09-catalog/cyclocross/cyclocross-series/09-f35x.aspx