A 2500 would bottleneck a bit at that point, it could run about 3 580s with no bottleneck. Two 590s just bottleneck a 2500, so...
Who told you so ? GTX 590s Quadfire & HD 6990s Quadfire were tested in a system equipped with the i7 965X, the articles didn't state any bottleneck.
And a member on Overclockers forums stated running Quad GTX 580s with 990X @ 5.0 GHz without any issue, 2500K is stronger than those CPUs. Also, a third or fourth card in CF/SLI doesn't add a much value for performance. So you're fine anyhow.