I have a speedohealer on the way, from what I gather it can fix the speedo to be exact like you say but the odometer will still be off, or you can set it back to stock specs. I have a 48 tooth rear sprocket so my speedo and odometer are off alot, speedo is off 25%, not sure how much the odometer is off, but it is off. I am going to set mine back to stock specs, I can live with the speed being off a bit, but I really want my odometer to be accurate.
I will let you know how it goes once it gets here and I have a chance to try it.