Pay the extra $$$ to get the max RAM your mb supports.
If you're keeping it for long term, then having the extra RAM would be beneficial to you since it's not user upgradeable.
You're coming from a Dell Laptop. Rule of thumb when using windows, the more RAM, the better your computer will run.
Since applications gets more robust when they release a newer version, they tend to be more RAM hungry.
I remember when photoshop was happy with 4GB of RAM. Now they're happier with 8GB of RAM.
It's better ot have it for " Just in case purposes ".
My .02 cents.
For avocational activities 8 GB RAM is more than adequate. Even the CPU intensive tasks that you indicate you might on occasion perform, a few extra seconds here and there (if that) will be hardly noticeable. Take into consideration that the new retina MBP has flash memory which will of set some of the differences that yone might experience with an 8GB vs 16 GB environment with a conventional HDD.
There seems to be an almost irrational obsession with speed at times when the fact is that far more often than not, the slowest component in the chain the the user. If the price differential will not strain the bank account, by all means go for it. It's almost like buying a Ferrari when one lives in Manhattan.