That much of a price difference, get the Sora group, 105 5800 is pretty awful anyway. Spend more on really good tires and you'll be better off than a "nicer" groupset.

Pounds heavier!

Most of the engineering that goes into higher level groupsets is figuring out how to get customers personally attached to the product, attaching significance to small incremental changes in weight and positioning in professional racing for maximum return on sponsorship dollar.