For me internal is bit (20%) slower than my high-speed micro sdhc.
The same was for Qole's EasyDebian - on microsd seems faster to me.
The other issue is that I prefer to have microsd corrupted someday instead of internal flash.
Access is the other thing - I don't know the influence if app uses data from mmc1 and utilize swap on mmc2 is it better or worse - I can't tell.