I just got my 2nd IGO-W. I have one drilled out to 1.6mm and the other to 2mm. I like the option to build single or dual coil. They were about $15 each here in the US, but fasttech has them for $6, although I do not know what quality the imports are. I will most likely look into a Trident next, since it has the adjustable airflow.
If you do drill out your cap, start with a smaller size first. You can't undo it. I made that mistake with my Octopus, before I acquired the desire for a larger, 2mm hole. Now, I really enjoy it.