BB,
I don't have any Buccaneer manuals to hand but from memory ...
In answer to your original question about take-off, you have to consider the unstick speed as well as the ground roll because you have to consider the rejected take-off and the stopping distance available. A blown 30-20-20 take off had a much lower unstick speed than an unblown 15-10-10 one, as well as a shorter ground roll. Therefore, on a relatively short runway, especially one without an overrun end arrestor cable, the margin between stop speed and unstick speed was much less for a blown take-off than for an unblown one. However, once airborne on a blown take off there was a margin of about 20 kts before a safe single engine flying speed was reached during which the only option if you had an engine failure was to eject. With an unblown take off you had safe single engine flying speed from unstick unless you were very heavy, high and hot; that is why unblown take-offs were the preferred option.
On the approach, datum speed for a given weight was 19 kts faster unblown with 45-10-10 than blown with 45-25-25. The problem blown was that if you throttled back even to minimum blow pressure (20 psi) you would have a very high rate of descent if you stabilised, and if you were fast and wanted to slow down you had to respect this minimum blow pressure. Also, you did not have sufficient thrust for a single engine approach. You could fly blown 30-20-20 and this was only 3 kts faster than 45-25-25 and you did have a single engine capability, albeit with relatively poor go-around capability. Therefore, if single engine the preference was to fly a 45-10-10 approach. Another relatively obscure case (and it did happen) was that if the airbrakes failed to open using the normal selector you either had to use the standby selector, which put the hydraulic system into emergency generating a lot more problems, or fly a 45-10-10 approach with the airbrakes closed because to fly the correct datum speed you could not use sufficient power to maintain the blow pressure if 45-25-25 or 30-20-20 without the airbrakes being open.
If you had a double generator failure you lost the 'cheeses' and so had to approach 45-0-0 which was 10 kts faster than 45-10-10; we did practise this and it was not difficult to fly, just fast (but then a Tornado in 67 wing approached at around 220-230 kts!). On my first landing at Gibraltar I had a 'cheese' failure and ended up 45-8-8. This concentrated the mind and, with maximum braking, I stopped in about half the runway length (ie. 3000 ft) so there was no real drama.
What a great machine to cut your teeth on! Happy days.