Use as many Autocannons and Battlecannons as you can in the first turn.
Have your troops spread out so that the Orks cannot advance from one unit to the next between phases.
Have counter assault squads nearby to trash the stranded Orks. Rough Riders and Command Squads w/ Flamers and Priests do very well in this role.
Several months ago, the local Speed Freak player actually got 3 Trucks of Boyz and 1 Truck of Nobs w/ Warboss into my lines unharmed. My shooting was terrible. But, after wiping out the units they caught, they were left out in the open. During my next turn, I proceded to destroy every model he contacted me with.
Massed flamers and reroll to hit power weapons will do a good bit of damage, even against Nobs.
Even heavy bolters can take down trukks. Autocannons are the way to go for guard though against his trukks. Don't forget that any blasts, including battlecannons, count as 2 hits against open-topped vehicles. A leman russ exterminator is what you really need, but those rules are in the codex anymore (but are in imperial armor I think). A demolisher with plasma cannon sponsons will ruin his day though (plasma cannons for trukks, demolisher for boyz and battlewagons)
With speed freeks its about prioritising targets, first destroy any transports as this makes them half a horde army, then bikes then buggies then the boys. Given the firepower of an average guard army you should if youre lucky only have to fight a few combats against ten man squads which are'nt unbreakable
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