Where I cannot personally comment on the 1600, I upgrade from a 1200 to a 1700 and would share a couple of thoughts with you.
First off, I was SUPER happy with the boost in performance I saw for various tasks. As far as gaming on older titles I really didn't notice much difference when using the same video card. I saw a significant difference in some of my newer titles. Many of the new games are taking advantage of multi core performance and you will see and feel a difference there.
One thing I did note, and you may already have planned this in your build, but what motherboard/chipset and how good are the VRM on that motherboard reviewed?
I personally had an ASRock Fatality on a b350 chipset. It worked (and continues to work) wonderfully for my 1200. I have a nice stable 3.8 OC and temps stay low even on the stock cooler. I liked the motherboard features well enough that I purchased another without thinking about the increased power draw of the bigger chip. What I found was that the 1700 requires too much power for the VRM to keep the R7 satisfied for a stable overclock. I ended up staying on stock clock for a while and just upgraded to a better motherboard this past weekend.
I would take a moment to look up some information on your current motherboard and make sure it has the power delivery to go all the way to the R7. In most cases/reviews I have seen indicate that almost all of the mid to high range B chipsets can handle R3 and R5 without issue.
So, short answer being that, personally, given where the prices are, I chose to go with the 1700, but it had a hidden cost down the road based on the motherboard I chose along with it. If you already planned that part out, go with the 1700.