When Steve Mastered Creedence Clearwater Revival for 33rpm, they used the same master for the 45 set. Everyone of Steve's masters that were used for both 45rpm and 33rpm, are the same. When Classic Records used Bernie Grundman's mastering for the Led Zep's 33rpm, they used the same master for the 45 set that came out later. In fact, all of the Classic 33rpm and 45rpm masters are the same. Again, why would they use a different master for the Metallica 45rpm? The same company released both the 33rpm and 45rpm versions. As you can see by my two examples, the industry standard. In fact, Every release that has come with both the 33rpm and 45rpm versions has used the same mastering. The Metallica release would have to be the only one in history to use different masterings. Just logic. I understand that you don't want to spend the money for the 45rpm set, but saying you are afraid it is a different mastering is just bogus. If you want the best sounding vinyl version get the 45rpm set. If you don't want to spend the money get the 33rpm set which sounds great as well.