Thank you all so much. I've taken the the plunge and brought the Hexanon so I may be the first to offer actual user experience with the Hexanon+CLE combo.
For anybody interested in this topic. My research shows that the Rokkor-M 90/4 and the Elmar-C 90/4 are best suited to the CLE and are actually good performers themselves. But I do need a faster lens so the options are the Tele-Elmarit-M (Light, good but flare-prone), the Elmarit-M (heaviest of all, but online comments show it's the best 90mm lens of all), or their older versions.
My budget is limited so I've decided on the Hexanon. Here I shall point out that Ken Rockwell's statement that "the Hexanon & Elmarit-M are selling used for about the same price" is not true. On ebay the former is roughly half the price of the latter. (I've also seen a lot of posting selling the old Elmarit under the Elmarit-M name but that's another story).
I've read his website again and he mentioned that Hexar-M lens should work on CLEs but further explanation is lacking. My biggest concern for the Hexanon is that (a) Hexanon lens are known to have back-focusing problems and (b) apparently any 90/2.8 lens wouldn't focus well on the CLE wide-opened anyway. Nevertheless I'll test it out and post the results here for future reference. Really thank you all so much for your inputs!