Aluminum head - stock vs prepped

Hi all,



I'd like to lose some weight - on my swift SE-1. I'm thinking alum head, but notice a large price diff between the 'stock' - http://ift.tt/1wEvs9r



and 'prepped' (on here ~$2k).



Now, I know that the prepped ones will breathe better, but my question is how much HP/TQ difference is there between the two?



Thanks,

Gary