Upgrade pros and cons?

[muzzer]

Existing PW site version 2.7.2 core running on php7.1. Site is perhaps 7 yrs old and never misses a beat. Can't speak highly enough about this solid version, but....

As new php versions are released (v8 in the next year I think?) and each seems to get quicker I'm looking at upgrading to php7.3 or 7.4 and upgrading the site to PW v3.x.

I've been away from the forums since v3 was released so don't know much about it. I guess it's stable as it's been around for ages now, but what I'm wondering is:

1. what are the real advantages of upgrading to v3 for a site which is actively used but with only periodic development. And what are the disadvantages if any?
2. Is there any speed impact (good or bad) in either general site speed under 3.x or admin-use speed/ease of use?
3. any issues with either PW version with newer php versions (>7.1) I should know about?
4. is there any good write-ups/vids about new features etc of v3 compared to v2.7?

Thank you