Really really depends.
Games like shooters, you need every split second to survive, so the adage of Lag = Frag comes into play. (besides it really isnt like (most) shooters are notable for their beautiful lush environments. (obvious exclusions such as crysis and farcry)
Effects, dependent on what effects. Shadows always seem worthless to me, excessive lighting and bloom is the same.
If its a game where the enviroments are part of the allure of the game, then a few frames per second is an easy sacrifice to make (environment such as Risen; but my god not the char mods)
Honestly... I played for the longest time on a PC that should have been in the smithsonian had it not been salvaged and frankencomp'd 6 ways from sunday, but now that i have a decent (IE 2 years old good) Pc, I rarely drop anything below 1900x1080 reso any more.
Reso makes it pretty and more crips, which adds too much to the visual appeal of anything, effects are just.. pretties. So I say, turn the reso up where you can, dump the effects where you can in order to strike a balance of FPS.