Not wanting to derail the conversation further but I have 1 friend who bought a specialized tarmac with ui2, had repeated issues with junction boxes failing, poor charge holding on his battery and then upgraded to SRAM (unfortunately with hydro) - he now has standard cable callipers and cable shifting and is happy. Another has just bought a BMC TMR01 with 9070 and is not impressed with it and wishes he had gone cable actuation. Another mate bought a SL4 tarmac with 9070 after his SRAM Venge got written off in an accident, he likes Di2 but notices no real difference compared to his SRAM in terms of shifting quality.
Di2 is superior for TT bikes, no argument, and if you shift under loaded uphill (I can't say this would be a frequent requirement)
re: the original question, Converting the frame for cable shifting would not be worth the trouble. You could weld cable stops to the frame, but if poorly done they would weaken the frame at that point. In fatigue related frame failure it is often the welds for the cable stops or frame drilling sites which are prone to failure.http://www.sheldonbrown.com/rinard/EFBe ... e_test.htm
Evo 5.63kg SL3 6.66 viewtopic.php?f=10&t=110579
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