It's impossible to compare that way, even just 1db difference is big ... easily enough to make your stage come forward and shrink the sweet spot. Proper driver integration will do more for your stage width/depth than you think.
To answer you specifically, I don't much care for that particular HiVi Kapton tweeter ... and I very much like the MDT-37. I'm not surprised at all you like the 37 even in your brief test.
Good ribbons however can do some amazing things, I think it's due to their superiority in the time domain. The RAAL I'm using now is I think the best tweeter I've ever used/heard, and I also have in the closet some Scan 7000 Revelators, 6600 AirCircs, Seas Crescendos, Seas Magnums, Morel ST1108, and Accuton C30's, among others. All of which are amazing in their own right, but the RAAL makes them all sound slow and smeared. Other ribbons I've used have also gave me that same feeling, like the Raven R2.1 and Aurum Cantus G1 ... although both of them have a touch of the 'splashy' ribbon sound, the RAAL does not. Another World Class ribbon is the Raidho used in Eben speakers, and available (although not listed) from Parts Express. I haven't worked with it, but have heard it extensively.
Domes it's harder to categorize, so many sound alike. But notables include the Scan 7000 - probably the fastest and most detailed dome I've heard. The Seas Crescendo and the cheaper T25 variants, incredibly tonally accurate and maybe the smoothest dome I've heard. The Morel ST1108 and MDT33, some of the most dynamic domes made. And the Dynaudio Esotar variants, although not commercially available anymore they have incredible detail AND dynamics, but not as smooth as the Seas tweets. The Focal TC120TD5 is also a great dome, fast and detailed, but demanding of proper integration and quality components ... but done right it can sound excellent.
Cheap domes, you can't go wrong with the Vifa XT25 ring radiator and the new double magnet version ... they're just so smooth, but a bit laid back and lacking a touch of resolution. The Dayton RS28a is a great tweeter, and a bit of a irony - an aluminum dome that sounds more like a silk dome. It has good resolution, but also quite smooth and musical. And there's a new Tang Band dome that I'm absolutely loving for the cheap price, the 28-537SH.
Is that enough recommendations for ya
