So, this is using my personal computer I mentioned at home. I am not so lucky to be able to use modern tech at work, which is typical with government related work. My personal computer is a 4700k (haswell) overclocked to 4.5GHz, with 24GB of ram, with one of the fastest SSD's available. This computer is brand new and eventually (remember this is a scaling issue, not incompatibility) sees the same issue as the others.
The key point, and this is one that the Sparx employee missed as well, is that you must look at the task manager view for the individual cores. Otherwise, you will think nothing is wrong at all. For example:
I take the example IBD, then grab one of the connectors then start moving it all around and don't stop. This computer actually shows now immediate issue at all. Check the task manager and you would think there is no issue as well:
26%? What is the problem?

Well, if you right click the graph and choose "Logical Processors," this is what you see:

So, while you do not see any initial degredation, only using a single core, and requiring a large amount of resources just to move a line around is a significant issue. When the processor finally does get behind, the lag is going to really start to kick in. This is because it is a combination of processor intensive, in comparison with similar 2d visualization tasks of similar hardware, and single threaded.
When the project scales, as I am experiencing, and/or you don't have the best hardware in the world available at work, as is my situation, the performance impact becomes significant. The result is that it is difficult to move objects around and lining up ports and connectors becomes a major chore.
So to prove the point, I did as I mentioned and created another IBD with 10 deep copies of the original IBD. I expect it might be more obvious that there is an issue. You can try removing them one by one and seeing when it starts to work like normal.
Stress Test Model
https://docs.google.com/file/d/0BwotitHXXmF5UlNGNVNsYW1zWWs/edit?usp=sharing