well, NearThewindymill, my PM targets require that 1) my year 11s are to hit their targets (currently averaging 1/2 a grade above them), 2) I get a 'good' or better lesson observations with the same group (not dropped below 'good with outstanding features' in years) & 3) I organise a shedload of extra stuff (boosters, mentoring colleagues, organising trips, that sort of thing).
I won't be getting the 5% you're so kindly offering because I'm at the top of the payscale & not eligible for further increments, but I'm happy not to take it anyway, given that my colleague with an extremely challenging bottom set year 11 is unlikely to meet the first two of hers, despite being an excellent teacher & working considerably harder than I have to with my nice, clever, top set.
Luckily for her, she's not eligible for a threshold increment this year, as she'd be unlikely to get it; HOD will make sure she gets a group with whom it's do-able next year, & it'll be my turn for a 'challenging' group.
which is only fair, but colleague's actually much better with the lower ability groups than I am, & enjoys working with them.
So my experience is: we do have robust PM, & generally that's fine, but it distorts all sorts of other stuff which is also quite important - like matching students to the person with the best skills.
It also doesn't reward the right people - there's no question that my colleague will have done more than me by June to earn any incentives going - & yet the data would have it that I've 'met my targets' & she hasn't.