Older vs. newer REL subs


Looking for any reports about older vs. newer REL subs.

I have a REL 328 (ca. 2013) which I bought used. It's a good sub.

https://www.hifiplus.com/articles/rel-r-328-subwoofer/

I would like to upgrade to stereo subs and I've found (finally) another REL 328 which would match mine. But, before I drop coin on that, I'm wondering if anyone has had experience comparing their older REL with a newer one. What's changed? What's better, worse, or the same? I'm considering the T7x and T9x lines.

Hoping for apples to apples comparisons, vis a vis driver size, type of sub (e.g. level of product line, sealed vs. ported, music vs. HT etc.) but whatever old vs. newer comparison you have much appreciated. 

Thanks.
128x128hilde45
@arafiq 
The KEFs are now gone, and the white sub doesn't go with the aesthetics of my room anymore. So the question now is whether I sell the white T9i and buy a pair of black T9is, or buy a single S/510 for now, and buy a second one next year.

If you end of selling the white T9i....please let me know.
Thanks for the recent comments. It's good to know when one is moving towards overkill in their room. So that could be one reason one would not spend an extra $1,000 for the S series. If there was a good reason to do it and I wanted to spend that money then I would do it. (If anyone would like to pay for my dental work I'd be happy to upgrade even further!

 I can see that in this thread there is a difference of opinion as to whether or not the S series really makes enough of a difference in the room that I have.

Some people believe that buying something of even slightly better quality is always the thing to do. But opportunity costs are real and so it's easy to spend someone else's money. That said if I could get the S series for two grand each and I had a very good acoustical reason to do it, I would do it.
@arafig 
So the question now is whether I sell the white T9i and buy a pair of black T9is, or buy a single S/510 for now, and buy a second one next year.
Buy a pair of black T9s and keep the white one. #swarm
@nmmusicman My Strata failed due to R8 failure. Poor design and there should have been a class action!
Below it was said that the T series from REL was aimed at home theater.

Watch this video on the S 510 and notice how often he mentions "home theater."

https://youtu.be/tN6IraLOjMg