The new 5800/6800/9000 calipers are claimed to have better stopping power, are lighter, have clearance for 28c, etc. For example:
"The new 5800 front derailleur has a longer link arm and a new spring mechanism when compared with the last generation component.
Shimano 105 5800 Brakes Features:
•Improved efficient and controllable brake system.
•10% brake increase in power (vs.5700).
•SLR-EV with new symmetrical dual-pivot design.
•Twin bearings reduces pivot friction.
•Compatible with 28c tires."
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"The older you do get, the more rules they're gonna try to get you to follow. You just gotta keep livin', man, L-I-V-I-N." - Wooderson
'14 carbon Synapse - '12 CAAD 10 5 - '99 Gary Fisher Big Sur