So, I did the upgrade to Sonoma yesterday morning. So far it runs Sonoma just as nicely as it did Monterey. Only been about a day now, but the Sonoma upgrade fixed the safari issues with closing additional website tabs, and seems to have stopped the random mail app crashes, for the mail app it may take a couple days to convince me it is fixed, but so far mail has not crashed once which is a good thing as that would get annoying when it decided to act up, usually in the middle of typing an email. So far so good with that too. Do not notice any slowness at all on it, it does have a 500gb ssd and 8gb of ram so should be golden.