That ebay workstation is in the US. Judging by budget in euros, that's a no-go, as delivery will be crazy expensive.
About getting a 5820k system now or waiting for newer CPUs - if you really need a workstation now, just get that 5820k
However cool the refresh might be, all the new cpus will also be more expensive. And by the time price drops, you can earn enough money to upgrade your CPU only (same X99 platform).
The new X99 models will only be official in summer, and probably get to retail even later.
