truggys is often based uppon the buggy couterpart so the gear ratio is the same, thats why the center diff use shims to make room for an bigger spur. in theory if you use some lubrication you should not see any extra wear

48mph is almost 80kmt thats pretty fast for an basher, im geared way lower than that on the exact same motor so watch your motor\esc temps, especially if you plan using 46t

Like your build it lokks real tidy