We started my sons racing career out on a Apex at age 6, shortly after and several thousands of dollars later we were tired of fixing the apex and made what i know was the best decision ive made since my son started racing when i purchased are first Cobra. There is no doubt that the cobra is the closest to race ready as any quad available. At 8 years old your son will adapt faster than you think to a manual clutch. The initial cost of a cobra will seem high until you try to make a drr,apex,predator or anyother cvt style quad compete with a cobra. If you look online at the race statistics you will see that cobras have been wiping up the 50cc - 70cc classes for years now and they will continue to for several more.
This is just my opinion based on my personnel experience. I hope your son continues to enjoy quad racing it is an awesome sport and is fun for the entire family. Here are a few places you can get more info and purchase cobra atv

pittmanracing.com
tittlebrothersracing.com
jannsenmotorsports.com

Good luck racing