any noticeable difference between OEM mount and top mount? minus looks?
OEM makes it easier to get the tank off on most bikes. The top mount uses the to front tank bolting points. You will have to take off the damper to raise the tank with the top mount. Its 2 bolts that you would have to take off the tank off anyway so there really isn't any added work.
There are no advantages or disadvantages to the OEM or Top mounts when it comes to the dampers performance.
I personally like the look of the top mount. Hyperpro's mounts and hardware are very nice quality pieces.