I have the LG GGW H20L 4 speed. It's over a year old now, but quite a good burner for both Blu-Ray and DVD. Never had any problems with playback with anything I write, but I always use Taiyo Youden disks (DVD) though.
Todays equivalent is the LG BH10LS30 which is 10x BD-R write, Microdirect have 'em for £87.
As for disks forget 50gb disks they cost a fortune. 25gb disks are around £1-£1.50 if you shop around (Scan had some good ones for about £1.20 each in a pot of 25).
You can get program like BD Rebuilder that will squash a 50gb disk down to 25gb, and also 8.5gb & 4.5gb for writing on DVD-R.
You can burn blu-ray films in AVCHD format on DVD-R disks with much higher quality than DVD but they need to be played back in a Blu-Ray player (or PS3). You can do this with a DVD burner too.
I use imageburn to write disks. In the settings you have to turn OFF the realtime verify in order to speed up burning on BD-RE (re-writable) disks. The options are turn on BD-RE/DVD-Ram fastwrite and turn off BD-R Verify.