I have m3i zero & SC DSonei, both with latest firmwares. Yes, DSonei is a bit slower than m3izero in booting up the games, but it's not a big deal IMO. You wait maximum 5-6 seconds more, but when the game is running, there is no difference at all. Honestly, you won't even care.
Loading depends on the game size. I have noticed my supercard being a bi slow lately but I play a lot of large music games, Band Hero (dissappointing game) and Lego Rock Band both take a while to load due to their size of over 200mb while other 30-100mb games still take about 10 seconds to load.
For me if you want to emulate the DS the best option is on Android, use DraStic and a controller that holds your phone... it's clunky but it works insanely well. The next best option in my opinion is using a New 3DS XL, not really emulation but hacked it works really well.