Hi,
I've had several extensive conversations with wix technical support.   I wanted to get to the bottom of which filter is best, and if there really is any difference between the 51515 and the 51452.  
 As explained to me, with wix, everything is application-driven.   The 51452 has a high burst pressure rating only because this filter is also used for transmissions.   And that is the only difference shown in the books (or on the web site), for these two filters, but that is only part of the story.  
 To summarize, the 51515 is really a car filter.   It is the filter to use if your IH never sees any bumps larger than the speed bumps by the schools in your residential neighborhoods.  
 However, as explained to me, if you drive your truck frequently off-road, along bone-jarring wash-board dirt roads, the 51452 is the filter you should use.   Both filters use the same media to filter your oil, with the same rated by-pass, anti-drainback, and filtering capacities, but the 51452 is the ruggedly-built filter, constructed to withstand prolonged and excessive vibration, and from a construction viewpoint, it is much more than a 51515 with a stronger can.  
 Remember, wix filter selections are application driven.   And if you do a check for the applications wix lists for both filters, you will see the 51515, with some exceptions, is mostly manufactured for cars and light trucks, while the 51452 is manufactured mostly for tractors, and off-road construction equipment, many with diesel engines and no suspension.   Other than a couple land rovers, I did not see any "car" applications at all in the 51452 application list, although the list is long and there might be some there.   As an IH owner it should make you proud that IH is the only light trucks rugged enough to be listed in the same category as the off-road tractors, excavators, etc.  
 So to answer the question "are there different grades of wix oil filters" the answer is definitely a yes, although that difference might not be apparent with a preliminary product specification search.  
 In addition, if that does not make you want to consider which wix filter is proper to use, remember that by using the filter they recommend for our IH trucks, if that filter should ever fail in a way that damages your engine, wix will repair or replace that engine on their dime.  
 As far as filter interchanges, don't trust the web sites or the books.   The baldwin b2 interchanges with the wix 51515, but that is as far as I will presently trust it.   If you're using another brand other than wix or baldwin, look in their application pages, not their part number interchange tables.   Baldwin, as a manufacturer heavy into industrial applications, has a potential to offer filters better than the wix 51452, but every time I follow-up on a table part number cross-reference, the specifications for the two filters are not the same, and sometimes are not even close.  
 I'll add another post here as soon as I receive the technical info I've requested from baldwin and have a chance to study it.  
 Other than wix and baldwin, are there any other major auto/truck filter manufacturers I should research?   (hastings and purolator are part of baldwin)
steve