the ryzen 8 core cpu could be near 2x faster, but only if all 8 cores are being used. otherwise if its using 4 cores or less it might be only slightly faster, or nearly the same if you have a high overclock on the i7-2600k. photoshop and lightroom tend to use 2-4 cores, so those programs will not see much benefit from ryzen 8 cores. premiere can use 5+ cpu cores and might see more benefit from having more than 4 cores, but it would depend on the project and media. so its still possible you wouldn't even see 50% performance gain with premiere.
for a new system build, if you want to keep costs down and are ok with overclocking, you could also look at the ryzen 1600 (6 core) or 1700 (8 core). if you do go ryzen you will want to get faster memory, around ddr4-3000. if you want to focus on photoshop and lightroom performance, then you could either overclock your i7 or go for a new i7 kaby lake. i don't know if there are any compatibility problems with ryzen or newer intel cpu's and premiere cs5, i'm not even sure if the gtx 1060 will work with cs5. you may have to search the forums or perhaps someone else will chime in with more info.
If it costs you $370 for a card that sells for only $250 in the USA, then blame your country's currency.
This would be a very decent upgrade at that total cost, however. If you went with a new i7-7700(K) build, then you would have spent nearly as much money overall for a sizable downgrade in overall performance versus the Ryzen build.
And by the way, I wouldn't recommend staying with Premiere Pro CS5. Nor would I recommend sticking with that GeForce 9600 GT. Both software and GPU are now obsolete; CS5 is EOL and will not see any further patches or updates while the 9600 GT is now also in Legacy support status (meaning that there will be no new drivers or future operating system or software support; for example, Adobe has discontinued GPU acceleration support for all Tesla architecture GPUs as of CC 2015.3)