I think Donnybrook might work well for this - especially with the author's 40K plug-in (which allows first-edition weapons profiles to be used with the rules).
It's a bit faster than some other card-based games, because whichever card is drawn from the deck activates a given character or unit rather than giving the player the choice of which to activate. It's a small but significant difference that potentially reduces tactical decision-making but does keep the action fast and furious by cutting out the potential for faffing around.
Essentially, the deck contains one card for each unit (or character). Whichever unit's card comes up next gets to activate.
Actually, you could port that activation system over to just about anything - from Song of Blades/MDRG to FUBAR to whatever. It sounds like a small difference, but the change from "OK, now you get to choose who to activate" to "OK, it's the cyborg sniper" is quite significant. It just cuts out the umming and awing and gets the game moving quickly and unpredictably. When very large numbers of players are involved, it's a huge benefit.