In response to your question about static pressure, this is what pressure drop the extractor can generate - the higher the static pressure, the better the performance will be as more resistance is added to the network. If you want to understand the physics of it, spend a few minutes reading about the Bernoulli equation on wikipedia. A high static pressure does not necessarily mean a high flow rate in a free system however.
The key thing to understand about dust extraction is that you have two parameters to consider - pressure drop and flow rate. Increasing the size of the ducting reduces the pressure drop for a given flow rate - so if your extractor is putting all its energy into overcoming losses in small ducting, increasing the size will be beneficial. With 4" ducting for the airflow your extractor will generate, moving to 6" will cause more problems than it solves because as CHJ says the flow speed (i.e. air velocity - as distinct from flow rate which is the volume of air moved) will reduce, and when the flow speed drops too low particles will drop out of suspension and start blocking your ducting.
To keep up with a table saw, especially one with a 6" duct, I would recommend that you look for a high volume, low pressure extractor (often called "chip extractors"). This is because with large ducting and big dust collection chutes like you get in table saws, what you want is a lot of flow rate through a flow network that has low pressure losses. For use with power tools, where the ducting and collection apertures are smaller, the pressure losses increase - so for that type of scenario you need static pressure rather than flow rate, which is why high pressure low volume vacuum extractors (which are basically big hoovers) work better. The disadvantage of a chip extractor is that fine filters cause a big pressure drop unless they have a lot of surface area, which is why you see them with such large filter bags which even then aren't very fine compared with what a vacuum type extractor can happily cope with. As you are apparently venting outside your shop though, this isn't an issue.
In summary - to improve your situation, fit a bigger chip extractor with a high flow rate and coarse/no filters venting outside your shop.
