As I recall, on the 75 pension scheme your pension was based on your rank not your salary (the band of brothers’ principle). People on PAS had there pension enhanced by a factor of X for every year on the PAS scheme. As it was a retention incentive, a minimum qualifying period of 5 years was stipulated. If you left before the 5 year period had elapsed you got the standard pension for your rank.
The 05 scheme is based on your salary, and as those on PAS no longer receive flying pay, all their salary counts towards the pension. I know of one air engineer who opted for the 05 scheme and left the air force one week later and got a full PA pension. (He still owes me several beers for the advice on that one.) I heard this was an oversight when the 05 pension was brought in, but a very nice one if your on PA spine.
