So I've been looking for a chair for quite a while and I've decided on a Herman Miller but haven't really chosen which model. For reference, I'm 5'8" 210lbs. I also live in Canada

I'm stuck between the Aeron and Mirra 2. I'd like to get them new mainly for the warranty and return if I don't like it.

I sit on my chair for a long time during the day. I'm a full-time student and a gamer so I can sit in my chair for up to 10 hours a day, maybe more. I have been experiencing pretty bad lower back pain for about a month now because of my old chair, now replaced with a placeholder chair which isn't much better.

At first glance, I thought they were the same chair with the Mirra being cheaper but I've learned that they aren't and have no idea which to go with because there are so many different customizable options... And I also have a few questions about both:

Mirra

1. is the butterfly back a must-have? seen many threads where people make a point to mention that it's included and make it sort of a deal breaker
2. what exactly does the flexfront adjustable do? the description doesn't make much sense to me
3. any reason to get the tilt limiter? I know for a fact that I won't use the seat angle thing but not sure how useful the tilt limiter is

Aeron

1. is the posturefit worth the extra $25 over the adjustable lumbar? looking at it, I don't see a reason not to get it for an extra $25 but just curious
2. Tilt limiter and seat angle worth it?
3. Is the Aeron worth the extra money over the Mirra 2?

Cheers everyone! I look forward to hearing your responses!