Aluminium Bed Thickness

Hi everyone, I've just signed up and hoping someone can give me a bit of advice.

I'm designing and building a printer from scratch and am wondering how thick my print bed should be. The bed will be 330x330 mm cast aluminium tool plate with a 300x300mm 750w silicone heat pad stuck underneath. I can get tool plate from 5mm thick and was thinking of going for 6mm as this should give me enough thickness for mountings threaded in around the 15mm border and I can also drill recesses from the bottom to mount thermistors in several places to check even heating.

Obviously thinner plate is cheaper and thicker plate will be more rigid and will give a more even heat but will take longer to heat and cool

What do you all think?

I want to try lots of different materials and have a very versatile printer with a build area 300x300x450mm so a decent size as well

Cheers
Ian