The AXIA is available down to 1.0GHz, making the 1GHz AXIA the best bang for the buck in overclocking. The AXIAR is available from 1.2GHz up I believe, so it is a little more expensive, but overclocks a little higher. The next newer one goes even higher, but is only available in 1.33 1nd 1.4GHz.
Cast not thine pearls before the swine