Hard to say.... IMO it would be more important what the flow numbers and flow charachteristics of the heads are.... Around this part of the country, there are some very fast Wissota Super Stock circle burner that are limited to 1.94 intake cast iron heads with a cast iron 5 barrel intake NON PORTED and running a 500 cfm 2 barrel carb.....

With the wrong combination of cam and heads, maybe the bigger valves will help, but on heads done right, especially on a street engine, I doubt there would be much difference at all in the performance between the two valve sizes... The valve size is just one part of the equation.....