I have added marking quote links to your own posts with (You), it's a hacked together javascript solution so it's most likely not optimal when it comes to performance. Though I did not notice any slowdown on my machine.
If there's a noticeable performance slowdown on your end, you can disable this via settings - > Other tab as with the images expanding on hover. It should not be an issue unless you are on an extremely old PC and made lots of posts.
Also this has no effect on network performance, everything is done on your side.