I note that most of the big pools offer VIP packages and a better payout rate if you have 10PH or higher...
It isn't actually a higher payout "rate", PPS rates will be same for 1TH vs 10PH, but it's a higher payout "total" as a result of a reduced mining fee which can range between 10% to probably 50% , the largest discount I got from Viabtc was 40% IIRC.
... however they don't indicate how much higher the payout is. Does anybody know?
They don't because =>10PH is a long shot, it could be 100PH or a 1000PH, so they expect you to negotiate with them, you could probably get some discount even before getting to that 10PH mark, most pools are operated by Chinese, they can be negotiated, heck! Binance even negotiated the listing fees and they went to as far as asking "how much could DGB team pay", and speaking of Binance, they now run a fairly large FPPS pool with 2.5% fees, so pools that ask for 4% will most likely give you a discount if you point say 2-4PH, you just got to try your luck and for that I wish you the best of luck.