Ah if that's your board, then yea the FX-8300 with the 95W TDP is probably the highest CPU you could get. From the looks of it the board's VRM is not good enough to handle the TDP 125W FX8320 and FX8350, so that's why they ain't listed in the support list. However, I don't think there's any retailer selling the 95W FX8300 in the UK. There are some people selling it on the famous auction site, but it's at £135.
Also, I don't think the 95W TDP FX8300 will overclocked as high as the 125W TDP FX8320/8350.
Yeh I had a quick search for an 8300 and quickly came to the same conclusion. I think it would be wasted on my board anyway like you say.