In theory, 400 grit US + polish will get more length and snap and be more susceptible to carrydown than P4000 grit matte.
In theory, they will handle similar (not indentical) amounts of oil.
The P4000 grit matte finish will be slightly earlier, with slightly less backend, with less of skid/snap and more of an arc-like breakpoint and similar amounts of overall hook.
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