Dex210 brushed motor gear ratios

[StuartH]

I'm giving my dex210 over to my son as he's getting a bit more interested in racing rather than just crashing

I'm going to swap over his electrics and motor as he has a nimh set up that he's familiar with.

The dex210 came with a 13.5t speed passion (which is too quick for him) I was going to put the brushed 20t motor in, or even a hpi 15t brushed.

I'm just wondering about gearing ratios for these motors. The stock gearing works out about 7.26 and I wonder if I should be heading more towards 8 or 9 or the other way around?

Just want to give him a car that's easier to drive and set up but still using the equipment he's got if goat makes sense???