In terms of performance there’s going to be zero detectable difference due to increased/decreased stiffness. If anybody can find credible evidence to the contrary please post. You never see industry data regarding ‘xx watts’ from a stiffer crank because no such data exist…you’ll usually see stiffness expressed as xx% stiffer…because the actual deflection numbers are miniscule even at four digit power numbers (deflection of 0.9 mm at 1800 W is 20% stiffer than deflection of 1.12mm. TWENTY PERCENT!! ha!)
In terms of weight savings…you know…buck a gram is the Mendoza line. I don’t know your specific case but usually cranks are a more expensive way to save weight. On the other hand it is an area where you can save a pretty good chunk.
From a durability perspective I’m going to offer an opinion that might be out of step with the norm: I find most branded carbon cranks to be more durable than their hollow aluminum counterparts. Over the past two years I’ve seen 4 hollow aluminum crank spiders just break off. Keep in mind that I ride a lot of gravel. In that same period I’ve seen three non-drive crank arms break off. I’ve seen zero carbon crankset fail.