I have long heard that Mesa/Boogies were drastically different from one run of amps to the next in the same model (like early Marshalls). The best Recto I have ever heard was when I saw John Petrucci at a guitar clinic in 1995. He was playing through a '94 Tremoverb Head. The tone was so damn heavy but clear. Thick and chewy yet a good bite and cut. The Rectos that I was able to play when a music store the next year in my area started carrying Mesa did not compare (though they are supposedly essentially the same amp with out reverb and tremolo). Of course my playing is no where near the quality of JP, but its important to note that though when I heard him play at the clinic the chops were his but the tone wasn't. It was quite different.
I was able to talk to him afterwards I asked him about the rig and he told me he never really played much through Rectos at the time, he was still very into the Triaxis rig but he wasn't traveling with his gear and the Tremoverb was the only thing that the music store could get on loan back then no music store with in 100 miles carried Mesa.