Sora is 9 speed, everything else is 10 speed, as you go higher up, parts weigh less and less, although the difference isn't huge, the feel is said to be slightly better in the better components (duraace is the highest, then ultegra, 105, tiagra, and sora, and 2200) people tend to state that 105 is the best bang for the buck and "good enough" for racing, hell I took my Tiagra racing, 25th out of 60 racers, collegiate level, having a duraace equipped bike wouldn't have propelled me to the top of the peleton. Having a well adjusted shifting system would make a larger difference than the component levels. $30-35 for a nice set of jagwire cables every half a year would yield better results than running the higher up groupset with cable changes every year instead.