The Sram Apex is equivilant to the 105 (from what I have been told). I have the Dolce Elite with the Sram and a Ruby Pro with DureAce & Ultegra. After using the Sram (got after the Ruby) I did't find the change to be a big deal at all. You are dealing with one lever instead of 2 on each side.

As others said, I would go with feel more than anything as components can be changed, not much you can change with the frame. For me I also tried the Giant Avail and I felt on top of the bike where on both my Specialized I felt as part of the bike if that makes any sense.