My son is starting to get right into L/B skateboarding. He has a 40" 10ply drop thru deck running 7" reverse trucks etc... and he's starting to do some reasonable hills and enjoys doing 'power slides'...

I understand that ABEC bearing ratings are an engineering measure of ball bearing & race tolerance (and not particularly relevant to skateboarding), so knowing that, is there much difference between ABEC 7 and ABEC 9 for cruising and down-hilling?

Currently running 90a compound bushes, but my son finds them too stiff - having said that, he's a big unit and blew out the 83a set in two days... will the 90's soften up over time?

Currently running 83a x 70mm wheels. Looking for recommendations on what to get next with a focus on sliding, as I can see that he's going to go through them before too long...

Thanks in advance...