I think that unless there is a large difference in requirements or other gain (such as commonality with something already in service), all equipment for the ADF should be sourced from the US. Mainly from the USN and USMC.
This should provide the best interoperability, service, supply and future growth.
Past examples I think the ADF should have bought are the M109 SPH and AH1 gunship. These could have been in service two decades ago, rather than a capability we are still waiting on.
The additional Helo's should have more Blackhawks and Chinooks rather than the MH90. Again a know solution in service now.
In terms of Land 400 I would look closely at the winner of the USMCs MPC contest for our cav vehicle.
I do understand where you are coming from as far as using US or USMC gear where possible, I certainly see the benefits.
My understanding of Land400 is for a highly lethal, survivable and networked combination of armoured vehicle capabilities and that the contemporary operational environment involves increasing levels of lethality and complexity.
As far as the MPC goes, the program was canceled in 2013 but resurrected in 2014 with the Amphibious Combat Vehicle program. For cavalry vehicles, the US are replacing the Bradley with the GCV program which is under considerable budget issues (I believe it may be shelved). Both programs are very much in the early stages and I think too risky, particularly considering previous programs for both vehicles failed. I don't see either entering service with the US before the relatively tight time-frames to get ASLAV replacements in service by 2020. I am not sure either are really an option.
From my understanding, I don't think the Stryker fits what we want to do with plan Bersheeba (particularly with protection). I don't see any major US options being leading options (although if the GCV is resolved it certainly could be in strong contention to replace the M113AS4 by 2025).
We have gone with non-us options before, and if we go options based on proven, in-service designs and can leverage other (albeit non-US) supply chains, I don't see the why they shouldn't be considered.