If I remember correctly, the Ewokgroomer release I downloaded was an ISO not an MKV. I only downloaded ROTJ, and it was a while ago, so I may be wrong.

The standard recommendation is to use Verbatim DL from Singapore not India, as they are the best (should say on the box). You use +R or -R based on what your PC uses I believe. I have always used +R.

TDK are not bad really - I use TDK single-layer discs - so if you have bought some, give them a try. If you've bought them, you might as well try them lol.

Why people make MKVs that are the size of DVD-5 or DVD-9 discs and don't realize that the size of the AVCHD folders takes them over the disc size is beyond me. I have had the same problem before, and if I had to burn the file to disc (I play content through a media player, so I usually burn nothing), I extracted the audio and re-encoded it to a slightly lower bitrate e.g. 448 to 384. This sometimes works, if the file is just over. Otherwise I transcoded the file, which sucks really, but I don't know what else to suggest.

I hope that someone more knowledgeable than I can advise you.