The 6:1 starter is using that ratio to overcome having a less powerful motor. It will work on either size flexplate. The Proform starters have to match the size of the flexplate, they're not a "one size fits both" deal, but they're more powerful.
Besides the battery voltage, the amp draw of the starter will depend on the armature windings/field strength and the amount of load the starter sees. It would be expected that a gear reduction starter wouldn't draw as much current as a non gear reduction starter all else being equal, due to the mechanical advantage it has.