Anand test the 4750G which is basically the same iGPU as the 5700G and it does perform a bit ahead of the 3400G. In addition the IMC in the 4xxx and 5xxx series parts is enough better than you can get good memory OCs further increasing performance.
I have a 2200G and am tempted to upgrade to the 5700G. My 3600 C16 b-die is vastly under utilised by my 2200G because it just cannot handle much above 3200 without issues where as I can probably get 4000 C18 out of it with a 5700G which on top of the clock increase is probably good for a significant performance increase in the games I play. Also the CPU uplift will help with Civ and the like.
I am disappointed that the 5700G is that far behind the 5800X and even 5600X when you throw in a GPU but I do think if they did some memory tuned vs tuned testing the APUs would close that gap somewhat.
EDIT: Also the 5700G uses less power than the 5800X so there is probably a bit of room there to increase clockspeeds a bit to also help close the gap.
I do agree that the 5600G is a better APU overall, the MSRP is also a lot higher, but the 4750G has both one more CU and a 200mhz gpu advantage, thats a significant advantage over the 5600G, the 3400G and the 5600G should be petty much tied on stock IGP perf. With DDR4-3200 the 3400G is the better APU for IGP perf check this, 3400G v 4350G v 4650G v 4750G with DDR4-3200 both stock and with iGPU oc. i have no idea of how to explain this, being wider with slower rams is actually better here, or maybe it is the 50% ROP reduction?
Expect the 5700G to be slower than the 4750G at stock, due to IGP freq being reduced by 100mhz.
So, TL;DR, with Renoir and Cezanne you need faster than DDR4-3600 to make a diference, for what i saw DDR4-4000 is the sweetspot, but dont expect to be night and day (compared to a 3400G than can easily overclock 200mhz and still gain some fps even with DDR4-3200).
So again, why they stopped producing 3400Gs, why they blocked it on the A520/B550? I just dont understand.