I'd go for Ultegra mainly because of the hoods being IMO a better shape compared to the 105s but only if you're happy spending just shy of another £200 to get Ultegra.
I'm told that Ultegra vs 105 is not just about the marginal weight saving but the operation/usage is slicker/smoother. I can't comment directly as I only have 105 but two separate peeps have told me this and one is a bike mechanic.