For the record, the Tiagra crank worked fine with the Sora triple derailleur and triple shifter. Just set the limit screws, readjusted the FD a little higher to accomodate the larger ring, and worked just like before. The upgrade is awesome, it is way stiffer, the 170 crank arms compared to 172.5 fit me better, and the larger chainrings give a better gear ratio. Now I just can't wait for the ice to clear to get out and put some heavy miles in.