...instead of the recommended 5w40 C3.
10w is less fluid than 5w at cold startup.
-30 is thinner than -40 at operating temps (100°C)
So less engine wear protection in both cold and hot
Of course, using a more fluid grade (-30 instead of -40 weight) will liberate some power in a pre race qualifying lap ( that explains the dyno results)...but will probably wreck an engine in a long race.
For a street car, sticking to the manufacturer's demand (5w-40 C3) is a bare minimum for engine protection.
Moreover, I don't even think that those modern engines benefit from more Zn like older ones, there are new metal protection layers lately, and new oil additives to match them (probably tungsten based, like Vanlube W324), that's why they recommend ACEA C3.
That nano additive-stuff, if Tungsten based, might not be so bad, but not in a new , running in engine.
An engine oil is a fragile balance, adding other stuff is not always a good ideea.