Most probably run the installed stocker Spur to start. Wait till you drive it first out the box and am comfortable with it. Gearing is very subjective. What works for some may not work for you. We all drive differently. Trial and error using some
extra Pinions first on hand is how its done. Cant be cheap about having extra pinions. How it is done. That's your call.
8s May be larger, but wont go Faster than a 1/8 Arrma platform by comparison. Do you have any of the 6s 1/8 Arrma's?? They are roughly 1/2 the weight of an 8s platform.
8s rigs are pushing a crazy 30+, give or take, Pounds depending on your chosen lipo Capacity.
They are a Very heavy Platform. Quite Overweight, IMHO. Probably why they break more easily.

Less forgiving with even moderate normal impacts.
Out the box you will probably get 35-40 MPH max. With a tail wind.....

Pushing faster speeds, will really take a hit on your run times. And ESC/Motor Temps will rise with Taller gearing. A Temp Gun and a GPS Speed analyzer are tools you will need.
Large scale platforms generally are not faster than lighter 1/8 platforms.