Intake install help- pic

You may as well cut it out if you're gonna use a standard composite intake manifold gasket. The exhaust gasses will burn slap through it in short order if it's not cut out. As stated previously, those holes in the intake and heads fit together to make up the exhaust crossover. It's purpose is to aid in a quick warmup. Closing it off will do absolutely nothing for driveability except make your warmup time a bit longer. The performance upside strongly outweighs any negative effects to your warmup period. Even in the coldest of climates, it will not have that great of an effect. A little longer warmup is all that you will notice. If you want it blocked off, either use the metal gaskets or go with the little block off plates you can get. I don't know where you heard not to use metal gaskets with an aluminum intake. The big blocks all have a metal valley pan that doubles as a gasket and people have been using those for YEARS with no issues. Somebody told you wrong.