I can tell you right now that Nidoking is a MUCH better special sweeper than physical (you ARE using Sheer force, right?)
Here is what I did for my Nidoking that I used at regionals for my tailwind team:
Nidoking @ Life Orb
Modest, 252 Sp.Atk 252 Sp.Def, 6 HP
Sheer force
-Ice Beam
-Earth Power
-Sludge Bomb
-Protect
Sheer force will negate the damage you take from life orb, while still getting the power boost. Sheer force will also make these moves AMAZING and will generally OHKO/deep red anything that doesn't resist it.
with that, Yanmega gets tailwind from the HG/SS tutor. Doing tailwind will let you use Tinted Lens to get round the non-effective typing. I would do something like this:
Yanmega @ Wise glasses/Choice specs
Modest, 252 Sp.Atk 252HP 6 Def
Tinted Lens
-Air Slash
-Bug Buzz
-Tailwind
-Detect
You don't need the speed investment due to the use of tailwind doubling your speed so that investment will be used so you can survive to get tailwind going and dish out the damage. Sure, there are other tailwind options (Whimsicott and Tornadus get it w/priority) but Yanmega is still a good pokemon to use it.
Hope this helps!