i can confirm that the SX610 is indexing really well and the barrel adjuster had a big part in that! i found that there was an unusual amount of tension needed to get shifting well. without an adjuster that wouldn't have been possible.

the only small problem is its travel. i'm not sure if it was designed for 6-speed, but the alignment in the low gear is not perfect. it's off by a few millimeters, so the pulleys are not completely under the largest cog. i'm pretty sure that has to do with the fact that i added an extra spacer on the right side axle to give the smallest cog more clearance from the fender stay fastener screws. no big deal...i hope.