Sorry, i was having a senior moment! So i guess the other question be could the nid player allocate any the skimmers cc to the gaunt (as would probably be advantageous) or is it technically not in b2b?

It's in B2B for all other rules purposes - removing ZoC, blocking disembarking etc.

I have always played skimmers (forcing FF) and opposing units in B2B to actually be in B2B for other rule stuff, like STM points out and hit allocation. I hope this is the right way. Hadn't really thought about it before but rather just assumed it to be so. Even if they're not fighting in CC they're still closest to the enemy at least (together with all other units in B2B of course).

How do people play this?

The Skimmer special rule only affects the opponent's use of CC or FF. Base-to-base effect still applies.

from 2.1.13 (my italics):

"Skimmers may always choose to use their firefight value in an assault, even if there are enemy units in base contact with the skimmer. If they do this then the enemy must use their firefight value also."

/Fredmans

This means that a Winged special rule would have to directly adress the Skimmer ability, and needs nothing else. Winged negates Skimmer, if in base-to-base.

/Fredmans

But this only for the unit in question right? Otherwise there'll be a lot of gargoyles accompanying bio titans... How much should this affect the costs of say, a harridan? Most other winged units have got better FF values anyway that I can think of.

I think a Winged special rule like this would have very limited effect; The main purpose of the skimmer wall defense is to prevent dangerous CC monsters (Carnifexes, Terminators, Daemons etc) from getting into B2B with FF specialists behind them. Forcing the skimmer itself to use its CC instead of its FF rating is a comparatively minor effect.

Well it would depend a lot on the opposition. For instance necron AV skimmers, destroyers and eldar jetbikes would be hampered a lot.