If "critical thinker" is part of the job requirement, you need to be able to measure and screen for that quality/capability.
If you can't figure out how to design your screening to objectively measure, sort, & select for that desired criteria, you have no business discriminating pay rates based on it.
And if you CAN & DO have a screening system that does so, you can prove you are not discriminating by making offers strongly correlated to scores in your screening system, e.g., "Strong candidates get offers $X-$Y, Exceptional=115% of Strong, Good=85% of Strong, Acceptable = 75%, lower=no offer" (presuming your screening system doesn't also include other explicitly/implicitly discriminatory criteria).
If you can't figure out how to design your screening to objectively measure, sort, & select for that desired criteria, you have no business discriminating pay rates based on it.
And if you CAN & DO have a screening system that does so, you can prove you are not discriminating by making offers strongly correlated to scores in your screening system, e.g., "Strong candidates get offers $X-$Y, Exceptional=115% of Strong, Good=85% of Strong, Acceptable = 75%, lower=no offer" (presuming your screening system doesn't also include other explicitly/implicitly discriminatory criteria).