I intend to do the same here. Given I was already CCSK but getting the latest version (4.0) of CCSK will be better followed by CCSP ( Combination of Cloud Security Alliance and ISC2)..
I would do the CCSKv3 right now. If you buy and pass the CCSKv3 right now, when the CCSKv4 is released in December 2017, you get a free take of the new test and a re-take. So you pay for one test voucher and get two tests.
I have been studying for the CCSK/CCSP since August. Two weeks ago I passed the CCSKv3 and it was very straightforward.
My CCSP exam set for November 13th. In December I will take advantage of the new CCSKv4 test.
It is not just the certifications I am trying to earn. It is knowledge. Taking the three tests on a similar body of knowledge six weeks apart will hopefully lock in the information for years to come.
Go for both. The CCSK is pretty easy to study for as it's based upon the CSA and ENISA documents. The information in both will give you many of the essentials for the CCSP. Additionally, if you have the CCSK the requirement to have worked in the Cloud for a year is waived.