sohc is a base.
there are no es that have a sohc, they are all dohc.
dohc has 10:1 compression, the tt has 8:1.
i have heard of only one single turbo conversion completed, and have yet to see it.
numerous dohc na motors have been upgraded to tt in a number of different ways (changing compression, staying with low boost levels, etc.) check
www.3si.org for a ton of info.
the fwd doesn't really seem to have too many issues with the power, although i would recommend replacing your differential.
hope this helps, safe travels.
- mike