Depends on who's 1640 you like to refer to...
Hardwarewise Sony 810 and DW1640 are the same inside. Firmware/front/bezel differs. BenQ firmware has gone thru many revisions (as already mentioned by geno888) and can thus be concidered as "better" than Sony's.
Keep in mind, every DVDRW drive is different, behaves different, burns different even when they are of same brand/model/revision. It all comes down to final factory calibration.
Noone can guarantee you good results because this (DVD burning) is not a "clone" science.
And there are many other parameters like; your HW/SW, burning application(-s), drives upper/lower filters, ambient temperatur, media, media temperature, wobble, phase of the moon,... did I left something out guys...?
But from what I've seen here and experienced with my two 1640's, these are some of the best drives you can own. Just remember to use good quality media.