Update - Finally got my gear and got the sensor installed!
It's only off a couple mph, but I think pretty much all clusters show like 3-5% over or something...? Don't remember where I heard that... What was interesting to me though is that the difference is in the cluster itself, the speed calibration on the scangauge in that picture is set to 0 so that's exactly what the ECU is seeing, which is right on with what the GPS reads. Part number for the gear is 32743-60Y16 and the snap ring 32744-35F00, they both work with the rockauto sensor if you go that route.