First of all, the price of two weigang 1G DRR2 memory chips is higher than that of a South Asia Yisheng 2DRR2 memory chip.
Secondly, if two memories form a dual channel, it is better than a 2G one.
Of course, if your weigang 1G DRR2 is 533 and South Asia Yisheng 2G DRR2 is 800, the speed can be improved a little.