I'm not into that much science but bigger is better. There is no bragging rights when you say you got stock size valves.
What I normally do when I 'rebuild' a head is replace the valves with 7mm stems [ABA] and install the 41mm intake valves since the stock ABA valves are really 39.5mm.
Not certain what options you have since you want to use a solid lifter head. For my driving style, I see no gains with a solid lifter head. I like the idea of a set it and forget it type of valve adjustment.
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