Lumping 98s and 104s together makes absolutely, positively, no sense.
The other divisions are pretty weird too.
I would recommend the following groups of common frame sizes based on how they feel:
- 90-93 (very precise but less comfort/forgiveness, especially when hitting with extreme grips, examples include the AG 4D 100 and PB 10 Mid)
- 94-95 (still control oriented but a little more forgiveness and easier access to spin, examples include the ProStaff 6.1 95 and AG 4D 200 Tour)
- 98-100 (giving up more control in favor of comfort and, in theory, spin)
- 104-107 (a lot less control, at least with 16 mains, but far more comfort and very forgiving)
String pattern also plays a role here. A 95/18x20 can play a lot like a "more forgiving 90" with respect to extreme control and comfort (eg PSLGT and AG 4D 200 are precise like the 90" AG 4D 100 while also being more spin friendly despite their dense patterns.).
My 98 PSGTs provide me with as much as control as my 95" AG 4D 200 Tours even though both have 16 mains. I believe the reason for this is that the PSGT seems to have the same height and width as the 95" 200 Tour and the extra area is concentrated in the "lower corners" of the frame and the PSGT has 20 crosses.
Only on Talk Tennis can you find people who believe
that 10 feet of lead tape has no effect on a frame...