I re-open it every month or so, and it didn't really change.
I can't notice it when I have 10-100 tabs open. It's unbearable when I have 1000 (which happens more often than I would like to admit).
It should be noted, though, that my web browsing machine is an early 2013 MacBook Pro with 8GB of RAM; It's possible I wouldn't have noticed on a faster machine.
On the same hardware, the same browser with TST disabled (and no auto-suspend) easily handles 1,000 open tabs - slightly slower than it handles 100, but barely noticeable. With TST it is unbearably slow.
I can't notice it when I have 10-100 tabs open. It's unbearable when I have 1000 (which happens more often than I would like to admit).
It should be noted, though, that my web browsing machine is an early 2013 MacBook Pro with 8GB of RAM; It's possible I wouldn't have noticed on a faster machine.