The R3 and the RS has different geometry, the RS has a higher front end but both should ride about the same. If you have a big belly or a bad back go with the RS, if not go with the R3. Both bikes should ride very nice. Make sure that the R3 has Ultrgra 6700 with the front cables under the tape.

You should also look at the 2011 R3 prices. The 2011 R3 has a number of improvements. http://www.cervelo.com/en_us/bikes/2011/R3/.

In addtion it seems that they cut prices for the 2011 models.
http://www.cervelo.com/en_us/bikes/2.../prices-specs/