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1. Shootas are superior in a footslogging list. Sluggas are good in Trukks, because they can get into combat quickly and without taking casualties. A Speed Freeks list like the one you have in mind would use Sluggas.
2. He's the most reliable Warphead you can take. "Oh I got 'Eadbanga even with my reroll? I'll change that to Squigify your Abbadon!"
3. Burnas are awesome with a Trukk. Lootas are awesome in general. Kommandos with Snikrot are nasty because they can come in from any table edge. "Oh look you got some Dark Reapers, here comes Snikrot!"
4. I use one. He rocks. 2 Skorchas and Grot Riggers and he's ready to go.
5. People will cry cheese when they see Ghazghkull kill off their Captain Lysander. People will cry in general if you field 45 Lootas.
Mmm.
6. I don't like Meganobs, so I'm not sure if they're worth it. Nobs with 'Eavy Armor, some
Pks, a WAAAGH! Banner, and a Painboy would be my basic gear. A Battlewagon for a transport is better for getting Ghaz and his Nobs there because Battlewagons are hard to destroy.
7. Speed Freek lists are viable, oh yes. I personally run a footslogging list but my friend runs a Speed Freek list and people find it hard to deal with.