I have a Phenom II X4 955BE @ 3.6ghz and dual Radeon 270X's in Crossfire @ 1200mhz core & 1575mhz memory and I've yet to experience a single bottleneck. My scores in 3DMark Fire Strike and gaming benchmarks (Sleeping Dogs built-in benchmark, Nexuiz built-in benchmark) are right in line with other Crossfired 270X setups with stronger processors, 5fps +/- difference max.
An A10-6800k's CPU portion is about on par with my Phenom II X4, so I wouldn't imagine it bottlenecking your 270X very much.