For large arrays, yes grep and map are slower than iterating the array. If you really get down into the weeds of perl performance, you'll find that any curly brace scope slows things down as well, so grep { $condition } @list is slower than grep $condition, @list.

But, the other posts here are the important bit - focus on optimizing your algorithm before you try to squeeze a few extra percent out of the operators you use. Knowing that map and grep are a bit slower doesn't stop me from using them in my everyday code, because most of my (primarily webapp) code is author-speed limited, not cpu-speed limited. In the rare cases where I want something to run faster, I whip out Devel::NYTProf and then look for the hotspots. Even then, most of the time the report clues me into problems with my algorithm, and I don't need to optimize expressions.