How many time of Memtest86 burn will consider enough burned?

Sold 2 sticks of Corsair pc3500 to A guy run on Nf7-s v2 and he runing at 250 fsb with 2.5-2-2-5 and at 2.7 voltage stable. But he want to run at lease 235 at 2-2-2-5 at 2.8 voltage. I told he already run 5 test with Memtest86 and pass. Don't know how many time you guys use to run will consider its enough? Cuz, i knew my stick never run with any burn test before and it only used twice. So, it consider new ram.

i run it for about 2-3 hours

Yeah, if mem is bunk or over-overclocked it usually shows pretty fast For some reason CPU's can be stable for hours then suddenly burp, but mem is picky.

--Illah