Sonic Classic turns out to be 64 MB unzipped as is, but Mario vs. Donkey Kong - Mini-Land Mayhem! is 32MB, and DSi enhanced. Someone try that and see if it works!
the actural rom size isn't 64MB,the rom size 16, 32,64,128 is for clean rom,however,there should always useless zeros at the end of the rom to padgen it to reach the 2∧x size