Sandie,
Having been so long out of the programme, any figure I gave would be a guess, but I think they're looking in the 55 to 70 knots airspeed region. Repeat warning - this is a guess. This would equate to somewhere around 30 to 45 knots deck speed, if the QEC can generate 25 kts WOD. Speeds would vary with assumptions/wind, ship speed, etc. As I remember, 45 kts WOD would be about the maximum for safe personnel ops on the deck.
I don't think an SSL would be cleared to an LHD deck, simply on account of the lateral safety margins required - unless they could clear the deck of aircraft, which is hard given their hangar capacity. Might be different on the larger LHA 'America' class deck, but probably still tight.
There should (in my view) be plenty of room on the QECs.
Standards have changed - an old friend of mine was a Sub Lieutenant Sea Vixen pilot flying off Hermes in the 1960s. Night deck landings gave a wingtip clearance of less than 15 feet from parked aircraft. In a Sea Vixen. Manual flying. At night.
I was just an engineer - God gave me c**p eyes, and in any case, I could never do what those people did back then. Huge respect.
Best Regards as ever to those who fly to the deck at night,
Engines