I did a test again with my computer under full load. I ran prime95 and the rhtdrbl tool which load both the CPU and GPU and I can hear only a faint trace of high pitched noise when I place my ear right next to the PSU. This is the same trace I heard when I am idle in Windows, there is no buzzing.
When I played Borderlands 2, I noticed no difference in the noise either. Regarding the GPU, Asus uses a super alloy design that should avoid the coil whine on the video board, they state: "Unlike traditional chokes, Super Alloy Chokes run 35°C cooler* and eliminate buzzing noise under load.", see: http://www.asus.com/News/1SEPpyJktCfBBHEj/
The MSI GTX 660 that I have does not state it has those special chokes like the Asus, but I hear no coil whine from it.
I understand you are disappointed with the coil whine you currently experience, but the Seasonic SS-660XP uses high quality 105C Japanese capacitors, why would you even try changing those and voiding your warranty? You can now RMA it and try for a new one that may not have any buzzing. Also, I doubt that the capacitors are the source of your issue, Seasonic already replied to silentpcreview as they identified the source of the coil whine in one power supply that was recently reviewed:
"Apparently, it is the quality of the winding process for the transformer that affects the noise I found, and this issue has been identified and corrected, with continuous monitoring assured for the future."
If anything, I'm impressed they are actively trying to minimize it.