Yes. Adding the ram will make no difference. Adding ram does not make a system run faster unless you just have a very small amount to begin with and you don't. Even in gaming, it has been shown that there is very little to gain between 4GB and 8GB. By the way, that memory you linked will not run at 800mhz. It will only default to 667mhz and you will not be able to change it because the Dell bios does not allow for that feature.
I upgraded a laptop from 4GB to 8GB and it made no difference at all, but the cost was only $20 for DDR3 so it was no big deal.