Originally Posted by dddd

Jim, the 6800 rear derailer is 11sp-compatible, I have one in my hands, very nice instrument!

So the OP could probably use 10sp chain with both his 9-10sp Gossamer and surely with the Ultegra-11 mech, however this newest generation of Shimano front and rear derailers have a significantly longer cable pull that any old friction shifter just might not be able to take up!

A 10sp (DynaSys generation) Shimano rear mtb derailer has an even longer cable travel than their road-model 11sp rear derailers, if you can believe it, but the 9-speed mtb derailers from Shimano will handle 9 or 10-speed chain perfectly, whichever of these chain widths that the OP (Friday) chooses to run with the Gossamer crank, and have a more-traditional (though not exactly short) cable travel as well.
I would not choose a regular 10sp Shimano road derailer to work with a 32t cog and with a compact crank, not to say that it couldn't be made to work ok.
If there is a 10sp 105 or Tiagra (mid-cage?) model that is rated to 30t though, It might be a good choice, and will have exactly the same cable travel as any Shimano 9sp derailer.