The 20g is just more of a good thing. it does have slightly, slightly more lag than the 16g. the 16g was only so popular because it was an off the shelf mhi turbo that fit the dsm and vr4 where the off the shelf mhi 20g was a tdo6 t3 flange and a different shape compressor cover.
If your having a turbo built look into some hybrid setups. Like previously mentioned, other more efficient compressors mated to a tdo5 turbine in your 14b housing and cartridge.