Really? Maybe the slowdown complaints were just stupid people who were slow in the head..."the DS games in the SC can suffer from slow reading speed that may cause slowdowns, frameskip in videos and slower loadings... " -> totally wrong.
If you like a G6 with 512mb go for it, it has almost perfect GBA support. If you don't care about GBA that much and want a lot more storage capacity and better support for slower flash memories, go for a SC Lite. Nowadays the games tend to be 128mb+, might be 256mb coming before the current year ends so I would never go for a G6 since it costs more and has no extra storage capacity.
Telling that SC lags is pure crap, M3 has the same problem if you buy a regular Kingston/Sandisk card. The Castlevania intro is just flawless with a regular sandisk if you have a SC Lite.
If you want better GBA support and you are willing to pay like 30-40% extra for that and some slow menus go for an M3 Lite. Otherwise I would go for a SC Lite.
You know for me about the space capacity..
I had a 2gb SD with like 35-40 games and you know what?
I only play with just five to ten of them (the ones with actual replay value, ie. MKDS) while the others just sit there and do nothing.. Guess it's just for convenience more than anything else though I still have to swap out games whenever something new comes out so it's really kinda pointless to have so much space to begin with.
Has Noobs that say 4 Gigabit/512 Mbit is to low, FYI, Who would want to stick Movies/Music their flashcart? I have 6 DS Games and 13 GBA Games on my G6, DS wasn't made to run music or movies.