In my experience against orks, it seems the more transports they have, the closer they get and the faster.
Transports can have 12 boyz if I am not mistaken, either way take as many as you can into one transport.
Roll the Nobz into the battlewagons with painboyz, put your warboss or whatever
HQ in with 'em, and just rush your opponent.
Since gretchin are very cheap to buy money-wise now, fill in the gaps of points with them to hold an objective. you can easily just block an objective with one big mob of those guys for at least 2 or so turns guarenteed