Is it ok to my system 24x7 @ this timings below continued

1648 MHz 6-7-6-18 1t @ 1.66v


1860 MHz 6-8-6-23 1t @ 1.68v


2020 MHz 8-9-8-24 1t @ 1.66v


Is Memtest v4.00 the best program to test my rams stability ?
How many pass should i have to run ?