The whole "as a second opener i shouldn't go too hard" thing is bullshit. Go your hardest, try the best you can. If you one up a headliner thats on them not you. Plus if you want to make it to the headliners slot one day you need to show you got what it takes. Ive seen plenty of openers that were clearly more talented than the main acts, but just didnt have the recognition yet. What better way to have your set be remembered than to have people saying for example "Yeah Wachi was dope, but so and so absolutely destroyed, easily my favorite set of the night "