I just recently upgraded my system from your EXACT configuration. I had, and still have, an FX-8320@4.5Ghz and a Sapphire R9 280, and upgraded to an i7-6700k. I still have the 280 currently as I sold my 290x and am likely going to go with a GTX 1070.
You should know that for gaming, the differences I see are like night and day. Everything is smoother, nothing lags, so long as I keep the settings realistic for the current card. Before, with the 8320, it did well enough, but there were some issues that are no longer an issue with the current configuration. The core performance is seriously improved and multi-tasking is a much less frustrating process.
As to the CAD, this is going to be a somewhat different matter and as IInuyasha74 mentioned, is really dependent on WHAT CAD software you are planning to run. Even what camp to select a card from might be affected by the particular software you plan to run. Listen to IInuyasha74, he knows a thing or two about what he's talking about and isn't going to lead you astray.