Oh please don't bake your cake at 400F! Cakes usually bake at 325-350F, depending on the recipe.
It's also a good idea to have an oven thermometer to be sure your oven thermostat is set correctly. Keep in mind that the temperature goes up and down regularly to keep from getting too hot. However, when it should be consistent and at the right temperature when putting your cakes (or anything else) into the oven.
By the way, don't pay much attention to the information given by Wilton. It's not the best and their food products stink, literally and figuratively. 
Michele
I normally follow recipes especially if it's the 1st time making a recipe. If they say bake @ 350, I bake at 350. I check the results and make adjustments if necessary.
What type of cookie recipe is it? Is it something that's suppose to have a snap to it?
I bake my cookies at 400. I make a thick cookie and dont like it crispy. I bake just long enough for it to brown on the edges and make sure the center is cooked and then out they come. I would say I bake them around 8 min. but I am usually making larger cookies.
Give it a shot and see what you prefer.
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