For anyone who does this, I went with the 3 M6 screws, one of which I had to cut shorter (I bought 30mm, 25mm would have been better). I figured the bigger size would provide more stability. I have also realised that the insert plate has to be fixed to the table too as the plunge mechanism lifts the plate right out of the table. I think I'm finding out why they tell you not to put plunge routers in router tables. I'm using a scissor lift as a height adjuster but may end up getting a third party add-on like the Router Raizer if that doesn't work out.