vivid mode are saturated enough... u add +3 for saturation summore.. the result will be bling blingg

"Hmm....  control the flash, you must. Manual power set, you use. Trial and error... only then good results you will get..." quote Yoda... 
I mean when using the external flash, try setting manual flash power to suit your environment. Test fire a few shots to get the optimal setting and then shoot. If you find you pics underexposed, then gradually increase flash power.

I do not understand what you mean by over saturated. Saturation means the colors of your pics. Are the colours too vivid? That's oversaturation and this is controlled by the creative styles and the flash has little effect on saturation. 

If you mean the flash appears too powerful and wash out the picture (overexposure) then it could be a matter of the flash firing at full blast due to dirty hotshoe contacts between your cam and the F58. Try cleaning the contacts with a blue ink eraser and try the flash again to see if the problem is resolved. 

seems like after u pp,the pix is better bro...for the 1st one the shirt is correct on the second one....same to the 2nd pix...the skin tone is better from my view....