You might also want to consider the Lite-On, if you buy a DVD-ROM. By default, it reads DVD+R, DVD-R and DVD DL at a speed of 8x, but there are unofficial firmwares available to unlock the speed at 16x for SL and up to 12x for Dual Layer media. Furthermore, it is considered as a good reader for hardly readable medias. Finally and most important IMO, it can do media quality tests for DVDs. True, the results are not as accurate as with some DVD-RW drives, but it will surely give you a good indication on what media burns fine with your recorder and in what speed.
As for the NEC-3520A, my experiance with the 3500A and the RIP-locked removed firmware, is that dual layer media is read at either 2.0x - 5.0x CAV, or 3.0x - 7.0x CAV. I can't tell why it sometimes rips at 2-5 speed only, but when it does, I can unlock it at the normal of 3-7 with Nero drive speed.