1.5V is pretty standard for regular DDR3... 1.65V for higher clocked kits.
You'll see in some of the profiles in CPU-Z that the Kingston 1600MHz XMP profiles are spec'd at 1.65V and the Corsairs are 1.5V for the same speed. The Corsair is the 'better' kit in terms of voltage required and 'better' from a timings standpoint too.
You should be able to apply 1.65V across the board. It's what the Kingston kit 'needs' for the speed, and the Corsair should handle it fine. Worst-case, try 1333MHz @ 1.65V and make sure everything is showing up correctly and work to reduce voltage from there.
As far as 'risky', anytime you run things a bit hotter or with more voltage, you run the risk of shaving some time off it's useable lifespan - but remember, it's off the end-state. RAM, at stock will run pretty much forever. When applying a reasonable voltage bump, DDR3 and platforms that support it will be long obsolete before that little amount of time you shave off it's lifespan will become a factor.
There is the argument for the chip and IMC with higher voltage but I've never heard widespread issues of issues with over-volted RAM (within reason). Have you owned the chip since new? If so, and you've always run at stock, then you should have absolutely zero issues @ 1.65V. If you bought the CPU used, then it may have been run hard and had excessive voltage pushed through it for years.... So any damage to the IMC may already be done. If you can't get it all recognized, at 1600MHz (or at least 1333MHz) with 1.65V maximum, then that may be the case.
In terms of timings, finding a common denominator can be tough - and you only have so much control over primary timings etc, other factors are at play within the BIOS that you don't have access to. That's why mixing & matching can be problematic.