To throw a spanner in the works, have you taken a look at the Canyon Ultimate Al? Pretty competitive weights for the price and they look pretty nice too...http://www.canyon.com/_uk/roadbikes/series/ultimate-al.html
Ultegra spec £1369 @ 7.35kg
Tour de France special means they're throwing in Sigma computer, 2x cages, 2x bottles, Topeak tool, Topeak pump, extra conti. inner tubes.
Could make for a pretty solid foundation to an Alu build.
If you were looking at stripping a F75 or CAAD10... From here looks like the saving of Force over 105 is 611g.http://www.totalcycling.com/component-weights.html
On the F75 that would bring you down to around 8kg, leaving you 1kg+ to find through the other components. You could stick in it a spreadsheet and see where the best savings per £ can be found by subbing in alt components. Force+ these components would probably start adding up price wise.