Well. Here's my experience.........
I was working on an FPGA and we wanted to transfer huge amounts of data from a 3rd party FPGA aquisition board, accross the PXI backplane, to an NI board for crunching. We couldn't use the NI streaming VIs since the technology is proprietary and NI wouldn't liaise with the 3rd party so they could implement it in their FPGA (which is fair enough). However. NI said that they could DMA at about 700MB/Sec in each direction (1.5 GB/sec) across the back-plane which was "good enough for our team".
The only problem was that all examples never addressed this sort of throughput apart from mentioning that, under the right conditions, it was possible.
So long story short. The local NI rep hooked me up with the UK FPGA guru. I sent through an example of what we wanted to do (with which I was getting about 70MB/Sec) and he sent through a modified version with comments about where and what was important in my example for getting the throughput. It could do it at 735MB/Sec (each direction). He also sent me through an internal (not for distribution) benchmark document of all the NI PXI controllers. what their capabilities where, what measured throughput's could be obtained, with what back-planes and which board positions within the rack (which is important).
Saying all that, It did take me two weeks to get through to him. I had to go through the "correct channels" first before the NI rep had a good excuse to "escalate" the issue through the system. The key is really building up a contacts list of direct dial numbers to the right people. If you know what you are talking about, they will be happy to take your call as they know it's not a silly problem. NIs problem is that there are too many inexperience people calling support for trivial things and, unfortunately for us, their system has been setup so that the engineers are well buffered from this.