If you like the NECs why don't you look for a 7550 or a 7551 instead?
You also have Toshiba and LG drives. The Toshs used to be very $$$$$$$.
Get one with DVD-RAM to cover all the formats - you find it with 7550/1 NEC, Tosh and LG.
Difs 6550 to 6750 must be in the speeds, probably related to DL discs also.