What in Wing Chun works the best?

[Ultimatewingchun]

...in all-out fighting/sparring against a skilled opponent? Not just your average streetfighter/brawler...and not against some guy with a year or two in whatever? art.

No.

Against people with real skills: boxing, wrestling, mma, karate, tkd, jiu jitsu, judo, sambo, muay thai, kickboxing, etc.

What in your experience works the best? In fact, here's another way to ask this:

If you had a "match" coming up with such a fighter from those disciplines listed above, and let's say he was skilled in at least one of the striking systems listed and at least one of the grappling systems listed...

What in wing chun would you be training the most for such an encounter?

What in wing chun would be on the list of things to really focus upon?

SLT ?
Chum kiu?
Bil Jee?
Wooden Dummy?
Chain punching?
The low front kick with the heel as the striking surface?
Pak as a block/parry?
Pak da (as simultaneous defense/offense)
Lop da?
Use of bong, garn, bil, bil/lop, gum, lan, tan as defensive and in some cases offensive jamming and structure/breaking and unbalancing moves?
What about the centerline principle would you focus upon?
The TWC Entry technique?
The TWC blindside strategy?
If yes, specifically what about the strategy would you be focusing upon?
Side (body) stance & related footowork?
Triangle stepping footwork?
How much chi sao would be part of your preparation?
Other chi sao/kiu sao related drills?
How much time spent on the forms?
How much time spent sparring?
Full contact?
Light contact?
Protective gear?
No gear?
Other things about wing chun not yet mentioned?
Some of the above, but not all of it?
If so, then what's on the list and what gets left off - and why?
Is there anything non-wing chun that you would try to include in your preparation?
If so, what?

AND FINALLY....

Suppose the guy you're going to all-out fight/spar is only skilled in a striking art - how would that change your preparation, if at all?

And the same for the other side of the coin: Suppose he was just trained in a grappling art?