1 generation 2.6, 5.2GB = 1x speed
2 generation 4.7, 9.4GB = 2x speed
3 gerneation 3x speed 4.7, 9.4GB
4 gerneation 5x speed, available soon

If you 4.7 or 9.4GB discs, it means that they will run at least in a 2x speed, unless otherwise mentioned as 2-3x speed discs(Maxell, Panasonic, IO-data)
Fujifilm's 3x speed DVD-RAM will be available soon(2003年11月10日発売予定 ) http://www.fujifilm.co.jp/dvd/ram_d.html

Recent price in Japan Market:

http://www.f-shokai.co.jp/dvddata02.html

http://www.watch.impress.co.jp/av/d...0904/ps_dvd.htm