I'm sorry, but science beats tradition in certain areas, and no I am not a Japanese sword practitioner..
I'm with icamanat95 about "modern" steel versus the steel in "any" historical Japanese swords when "forged in the same fashion". Superb japanese swords have been made throughout Japan's history, however when talking modern pure steel overall "strength" and homogenous integrity versus Japan's historical swords (regardless of maker), there is no comparison. I'm sorry, but you CANNOT refine marginal iron ore through japanese traditional methods to the purity and molecular specificity of modern steels. PERIOD. The master swordbuilders might get close, but never even.
Now the masters might have built a better Japanese sword that handles better or is prettier, but in actual steel, modern steel is better period, whether folded and heat treated in the traditionally manner or not. That's science and fact.
As to the "beauty" in any of the Japanes swords, this was more an accomplishment of the polisher/finisher than the sword blade maker. Much of the beauty the polishers bring out in the Japanese swords is actually DUE to the impurities of the metal.
ANY sword maker would want to start with the absolutely best metal available and if Masamune were alive, he would also demand the best modern steels to start with, however he didn't have them. He made marginal iron into beautiful efficient swords, but if he were to make one using modern pure steels, it would be much stronger. It also wouldn't look as pretty since it would be missing the impurities that make them so pretty.
As to Clark versus a real Masamune, if the whole purpose was to smack the edges of both swords directly against each other to test steels or see how far you could bend one before breaking, and nothing more, I would lay odds onto the Clark sword being much tougher with all things like thickness, weight, length, and edge sharpness.
I can't speak to the handling and balance of Clark's or Masamune's swords as I am not sword proficient.