A Mori poll did show that many teachers quit after 5 years due to the nature of the job.
I quit after six.
Like you I had responsibility points.
Like you I was pretty much top of the pay scale.
Like you I was burnt out and this was flagged up by the dread in the pit of my stomach at the end of Sunday night or holidays...
...and the fear - in spite of both good Ofsted and good results, positive residuals etc - that I would be 'found out' that I wasn't much cop after all. The job can really make your self esteem suffer especially if you haven't worked in a cross-section of schools.
Like you I had a supportive partner to support me financially.
Like you I wanted a career change and to see what else was out there as I feared I was 'institutionalised'.
Like you I worked in Manchester.
I have read Help! I'm a teacher get me out of here! and the Frank Chalk blog subsequently but when I quit I had just had enough. I had tried and failed (self sabotage on two occasions) to side step to another school so when May came round I too thought Life is too short.
I ought to point out we were double income, no kids at the time and also had no mortgage.
So what happened next?
In the eleven years that have followed
I tried and failed at call centre work/working in IT
I tried and failed at cold calling work/sales and recruitment
I did supply work and realised how good a teacher I actually was and also how easy I had had it but not realised at the time
I considered community police service and midwifery but had a child by this time and couldn't do shift work - had done adult ed at night but did not see it as long term option, more an add-on when had no kids
I looked into traveller's education, outreach sex ed, museum ed but did not have the right experience
I applied for literacy and support roles including non-teaching pastoral but was overqualified, not qualified enough or passed over for internals/admin
I considered just being a teaching assistant for a while and did some of this on supply and inclusion work
I considered retraining for primary to find I couldn't actually do this but did do some primary on supply but number of jobs competitive
I did some long term maternity cover
I found supply work was paying 18k per year and work was drying up due to learning cover supervisors
I became a learning cover supervisor
I emigrated
I became a postman
I taught a bit of language school, a bit of private tuition and primary age group for a while.
I am currently on maternity leave but am a minimum-wage childcare creche worker. My partner is the 'breadwinner'.
My CV would look like a downward spiral and I would and will seriously need to buff it/explain my choices.
Some decisions were poor but it is easier to regret stuff you do rather than stuff you don't. Some decisions were influenced by pregnancy and some by sheer bad timing.
Beckett: ever tried and failed? Try again. Fail better.
What I do know:
Supply work is not easy nor constant nor lucrative, not any more.
A career change with further study involved better sooner than later.
If you are a born teacher you can leave school but it will never leave you!
If you put your partner in the financial support role you cannot complain if you find yourself the SAHM/homemaker.
Similarly he shouldn't resent you for it or throw it back if it was offered willingly at the time.
You need to keep up with new developments as teaching and the bs that goes with it is ever evolving.
You need to decide whether it is the job that sucks or your school or SMT/colleagues that suck more.
In hindsight knowing all I know now I would have changed schools first probably a couple of times before giving up on my career or I would have changed my responsibility/stepped down for a while (part time is for me half the pay for twice the hassle but not for everyone. Cover supervision is easier if you don't mind full contact time for 18k salary but easier if you know the school and the kids).
What I really would say to my 20something self would have been:'
You are good at what you do.
You are good with kids.
You worry too much.
You are doing too much.
Stand up to SMT/line managers/hod if unfairly criticised.
You know more than the average Ofsted inspector.
Strive to balance work and life - the odd book going unmarked or by the seat of your pants lesson is not going to kill you.
However if it is affecting your mental health to the extent that you cannot bear another day then it is a no-brainer: You get out (and live with the consequences later down the line if you do not find a viable alternative).

I hope my essay has not bored you too much or depressed you. I think I could go all the way i.e. management were I to re-enter the profession now - knowing all I know now - but that is the glory of hindsight and experience and besides my CV is now fucked diverse 