Video will be slightly higher (slightly higher bitrate), but the biggest difference is audio - the MKV includes higher quality main soundtrack (lossless, I believe - at least in the cases of SW and ESB) and several more tracks for different languages.
So not REALLY worth the investment in a Blu-Ray burner then? Sound isn’t amassive issue to me as I only play through a sound bar or TV Speakers anyway.
I work in a theatre and got some friends together to watch SW 2.5 AVCHD on the BIG screen. I couldn’t A-B it with the MKV, but I seriously had ZERO complaints. Not sure if it’s worth the investment. Unless you want the extra gigs to be able to have a BR with a fancy menu and extras, etc…