I would go 105. I actually run an Ultegra 6600 (10 speed) FD and RD with a 9 speed chain and Tiagra shifters, crank and cassette. The set up works MUCH better than my old Tiagra RD and Sora FD set up, even though it could be considered a 10 speed 9 speed mismatch. I would imagine the 105 would give you much the same experience I have had with the Ultegra, which is crisper shifting and little need for derailleur adjustment. This will give you the option of eventually upgrading everything to 10 speed (which I plan on doing after this season).