Yes, it definitely will increase the performance. Faster memory speeds are a Definite YES, for an APU. If your motherboard supports 1866MHz then go for 1866MHz instead of 1600MHz. Since, GPU has access to the system memory and does cache Data... you will benefit from the faster speeds. So go with GSKILL TridentX or RipJaws or Corsair Vengeance Pro. Good luck with the memory upgrade.
Am guessing the DRAM you have IS 1600 - if it shows freq as 800 - then since DDR3 is DDR (DOUBLE data Rate) it's take the freq 800 x 2 = 1600 effective - which is what you are looking at - there is no rated 800 DDR3 - 1066 is the entry point