4 GB is fine for gaming. Using the verb 'need' is very misleading. Maybe 'want' would have been better.
@OP I have 16 GB, I don't run as many heavy programs as you but my system tends to have a good 4GB in use and 6-8 GB in reserve allocation. If I want to run a game that's another 2-3 GB. Personally I prefer to have as much RAM as I can afford after I've hit my goals on the CPU/GPU. I also run opensource OS's though which appreciate a lot of ram (caching all those libraries ftw)
I can't see RAM being much cheaper than it is now.
In real world terms, does this whole faster/slower RAM actually mean anything though? In benches sure, but I didn't think for 99% of users it made any real difference. 32GB 'slow' is still going to trump 16GB 'fast'.
Go for 32gb if you got the ££. otherwise stick with 16gb.
just remember windows tend to create a pagefile the size of your ram (which can be adjusted) so make sure you relocate or spread the page file across many ssd's.
The new Mirror's Edge games has a recommended spec of 16GB RAM.
So 32GB for a bit of future proofing is perhaps a good idea whilst prices are good.