I find it difficult to get a true reading of the High Evolutionary's power. He somewhat evenly fought Apocalypse during the Evolutionary War, but at the same time said he could fight Uatu if he had to. He fought a hungry Galactus, but didn't do very well. He was also overpowered by an semi-resurrected Forsung. During Annihilation Conquest, it was suggested by Moondragon that Quantum Bands are nowhere near enough to fight the High Evolutionary.
He's also had some low showings. The Man-Beast has given him trouble, and in one instance slashed his throat. He seems to skyrocket and wane in power depending on his state of evolution.
That said, he has what appears to be the best man-made armor in the Marvel Universe, which can reconstitute his body using stored DNA data, evolve him to near-godlike status, de-evolve beings, grants him a measure of super-strength. He laid out the Grey Hulk pretty easily, IIRC.
If there anyone that can match his armor, and on what level do you place the High Evolutionary?
I think that his power-level depends on how crazy he is. When he seems to be crazier (During the Evolutionary War saga.), he seems to be at his most powerful. When did he say that he can fight the Watcher (I mean, anyone can fight him, but he wouldn't WIN!)? Again, sometimes he goes through crazy periods where he thinks that he can do this kind of stuff. As for his most impressive stuff, he did create Counter Earth all by himself. At the very least, he's extremely crafty and smart.