6gb vs 8gb of RAM in a laptop?

Ok so I am getting a Laptop sometime soon and my budget is $750. I found a coupon for HP that takes $350 off of a laptop priced $1099 or more. I am at wits end attempting to determine whether or not to get the RAM upgrade from 6gb to 8 gb for $100. I think that the increased RAM will allow me to keep the computer for a longer period of time before it becomes obsolete. The problem is that the upgrade will put me $100 over my budget. The smooth operation of my system is of utmost importance. Would it be in my best interest to either wait a little longer and save the money or borrow it from my parents, or should I just stick with 6gb of RAM? I know that CPU speed and amount of RAM are two key components when it comes to speed and power of the computer. If getting the extra 2gb of RAM will allow me to use this computer for an extra year or so then I think it best to upgrade. Please explain both the advantages and disadvantages of each option. Thanks