I personally believe you should ALWAYS turn the Mastering Presets off when comparing arrangers. Personally, I believe there is too much compression and too much jacking up of the low end in Hammer's examples. Don't get me wrong, that's probably how it came OOTB (set up to sound decent on wanky cheap speakers) but if you ever want to compare apples to apples (Granny Smiths to Golden Delicious's!), listen to them all without that junk applied.

Or at least make the effort to copy the same settings to both.

I am still waiting to get my friend's BK-3 back (although I think he is trying to swap it for a BK5 so he can use an expression pedal) so I can definitively listen to it alongside my BK-7m.

Just from general listening, I felt the BK-3 had much shorter loops in many of the samples, or fewer samples (stretched further) to give it an overall loss of vibrancy and depth to some of the sounds. But, OTOH, much of it seems pretty much the same, including many of the great drumkits. But until I get them back to back, I'm not prepared to stake my life on it.

The BK-7m and BK-3/5 have a lot of styles in common. It ought to be a quick job to play them back to back with their Mastering effects off, and see what the TRUE difference is.