3DMark
3DMark is the latest version of this hugely-popular synthetic benchmark. Making use of DX11 features such as tessellation, compute shaders and multi-threading, it provides modern-day results and is available as a free download.
The overclocked R9 290X cards from Asus and PowerColor ship with the same frequencies, and as expected performance is nearly identical. The PCS+ has a slight edge, but there's very little in it.