Just a little update, after my Mot I had some high flow cats fitted 200cel. The sound is awesome, no drone at all in my opinion. Can't post a sound clip as it doesn't let me lol.
I would get rid of the de cats really, they cause drone as has been said above you can try hfc's but stock cats would bring the drone down but also the noise. I have just fitted hfc to my gemini exhaust on my 370z and I get no nasty droning at all.
There is in my opinion no drone with my Gemini and high flow cats. At around 70-80 mph you can talk to the person next to you if you want to haha. But when you step on the loud peddle it sounds awesome! Buster bob has the N1 and he says it's nice, but he has standard cats I think.