i'm also very happy with this board !
(reminder
GA-MA790XT-UD4P with latest bios from site (F5)
sapphire 4890 vapor-x
4 gb dd3-ram (kingston value) rated @ 1333mhz
X4 945 (3ghz, not BE so locked multi of 15)
corsair hx650 power supply

this is where i'm at now:

15x250 = 3750
10x NB = 2500
10x HT = 2500
PCIE = 100
memory at 3/8 (so mem running @ spc)
ram @ 7-7-7-20-27-2T (auto)
NB voltage = +0,2 (1,3 total)
SB voltage = unchanged
CPU NB VID = +0,125 (1,3250) (not quite sure what this does though)
CPU voltage = +0,200 (1,45)
cpu temp in de gigabyte monitor were around 55-56° (case 43°) at full load

all of this is 1h occt-stable and several hours prime-stable, cinebench-stable and 3dmark vantage stable so that seems good enough for me

if i'm looking for real-world gaming performance, what should i still try to change or increase? Also, do some voltages seem to high? Which ones can be lowered without hindering performance / stability too much (or which ones should i start playing with...)

thanks !