Originally Posted by Primo Tiki
Ultegra = Stiffer + Lighter (980g vs. 777g) = Faster
A 172.5mm 6600 Ultegra crank is 840 grams with the bottom bracket (weighed by myself on a triple beam balance scale).
According to Weight Weenies a 175mm Gossamer Compact MegaExo crank with bottom bracket weighs 909 grams. Add 10 extra grams for a regular crank vs. compact and the total is approximately 920 grams.
That makes the total difference approximately 80 grams (or less than 3 oz.).
Also, usually heavier means stiffer for the most part if that's important to you.