I know for 2016 the 105 group set received 2015 Ultegra's upgrade. Not sure if the 2016 Ultegra set was updated or not, but you are likely not to be able to notice the difference anyway. I have no issues with my 2016 Synapse Carbon Disc 105.
Also I would consider parts availability when chosing between these two brands. Even though Cannondale is not known for best customer service, still it is a local brand with parts warehouse in the US. Not sure what the support is for Stevens brand.
1lb weight difference a factor? Not for me. I can loose that much by skipping dinner one night.
Good luck with whatever you choose.