Charles. The cost of 4" trunking and gates was the deciding factor in going for the 62mm, as well as the fact that my work area is so small, the big 4" just pushes everything too far off the wall.
I cant run it above because of all the shelves. It does all work well (when the gates are closed properly).
I have a domestic vacuum cleaner tube and head on one of the gates, and it can take up an amazing amount of dust and chips from from my router sled table.
The router pipe is split after the gate with a home made Y joint (nobody makes one), to get suction to the fence as well as the router cabinet, so the total area upstream of the gate is much greater than downstream.
Its not ideal, but I have to juggle space and money, and in all other respects its a good system for my needs.
I've searched and found I am not alone with this problem on plastic gates. I was thinking of slicing off the rear section so the vacuum pulls the blockage free, but am worried that will just give increased air losses when its opened. I can just about swap the router gate around so that the plate hangs down rather than horizontal. I'll do that and see if theres an improvement. The gate is very stiff, so it should stay closed when pushed home. If that doesnt work,I will have to get drastic with home made.