I got my hands on the GM last week for the iPad. Its like owning a whole new divice. I had it jailbroken on 3.2 before upgrading and I find it not jailbroken with 4.2 a much smoother experience on the iPad.
i have to agree. even with a very small amount of jailbreak apps installed on the iPad made it feel sluggish at times, and iOS 4.2 background processes feel so much better on the iPad than Backgrounder did.
I will still be jailbreaking my 4.2 iPad as soon as the break is available, mainly because of a number of choice apps I want to have, namely: FolderEnhancer, Parallax, WeatherIcon, Shrink, Infinidock, Iconoclasm and FullForce.