I got very lucky recently and scored a set of the 660 gti mids brand new for a great price. Had been looking for a few years. They are really awesome drivers. If one can find them do not hesitate...I've come to the conclusion that the JBL is still the driver to beat when it comes to pure unadulterated fun in a 2-way.
it doesn't have the throw that the SI TM65 has, but I haven't read where it struggles with the upper midrange/lower treble and that has been noted by multiple reports here.
And if I "wanted a little more" so I can "cut where needed, instead of boosting" or generally just needing that higher output all the way up to a 2.5Khz crossover, then I would have to always defer to the JBL, either in 660, or earlier Gti offerings in the 6.5" frame size.
I think a lot of people will be eventually letting go of their TM65's that they've lusted over and once installed, were underwhelmed unless they were using them as mid bass with a nice, niche midrange inserted into the speaker column.
but that's just an opinion, and everyone has them.
It's going to be harder and harder to find a pair of 6.5" JBL of the 600Gti or 660 series, with these kind of posts.