Your 105 group is just fine and will not slow you down. There is no generally agreed upon "sweet spot" for groups, as people have different priorities. If you are interested, you can search for similar threads, they pop up every couple of months. Not long ago there was a Bikes Direct fanboy who was insistent that nobody needed components nicer than Claris. Enjoy what you have, and if/when you decide to upgrade, that's good too.