I know this an older thread but i think it's still very relevant as millions of 10 speed bikes are getting older and need upgrade and 11 is the new platform. I just tried this scenario with 5603 105 triple shifters and new 5800 double derailleurs front and rear. Front shifts well but requires the entire stroke of the triple shifter to shift the 1 cog of the new 5800 double crank. The rear does not work well though. You can get about 7 or 8 cogs but you can't get the whole 10 speed cassette with the 11 speed rear derailleur. The pull rate is slightly different. I researched this and read elsewhere that the pull ratio would be the same in 11 speed as 10 but it doesn't seem to be true. As an aside for others blending parts the 11 speed front derailleur and crank shifts great with conventional 10 speed chain. I had bought a new directional 11 speed chain thinking it'd be needed for proper front shifting but it's still in the box.