I have compared the Celestron Regal M2 80ED with the Vanguard Endeavor HD 82A. The performance of the Celestron is much better. I couldn't see a big difference to a Pentax PF-80EDa but the Vanguard could not compete. A great advantage regarding the Celestron Regal Me 80ED is it's compatibility to 1,25" eyepieces which offers nice alternatives for those who have astro-equipment. I think that the Celestron Regal M2 80ED is the best choice for those who can't spend much for a spotting scope even though they need high performance. From 20 - 40x it is almost a good as much pricier upper middleclass spotting scopes.
http://www.photoinfos.com/Spektiv/Celestron-Regal-M2-80ED.htm
http://www.photoinfos.com/Spektiv/Celestron-Regal-M2-80ED.htm