Ike
Tony is right.
I have been using one of the B&Q models and it will switch 2400 watts without any problems - just like it says on the label and in the instruction sheet that comes with it. My router will give it a good work out everytime and there have been no signs of trouble at all and that is rated right on 2400 watts. Sucks up dust very well, too!
As for the filter question, I reckon 0.5 microns should be good enough. That is what the filter manufacturers recommend unless you want to try for something out of the ordinary. You have to remember that the finer the filter the faster it will block up. When that happens you will have no filtration at all, and very little extraction.
It is a case for compromise, really. There will always be some dust in the air despite our best efforts. However, there is always something nasty in the air, anyway, unless you live on the top of a very high mountain! Pass the oxygen!
Come to think of it, the only safe way to do any job that involves cutting something is to wear breathing apparatus. I've done that often enough to know that it works but it's not practical for woodworking!
Cheers
SF