"Trade-off to consider:
If you use race pistons with valve cutouts in the dome for non-interference, a DOHC Subaru motor will still bend a valve if you ever lose a timing belt. This is because the separate cams on each head can free-wheel, allowing the valves to collide with each other. This can ruin your weekend and cost lots of time and money. So make sure you inspect your timing belt annually, and replace every 2yrs regardless.
If you use similar race pistons with valve cutouts on a SOHC motor, you won't bend valves if you lose a timing belt. Just simply replace the belt and you're back in the dunes. Losing a belt is not a common problem, unless you don't inspect it annually. But if you like the safety of the SOHC setup, the trade-off of protecting your investment may be worth having a little less HP. But remember, SOHC motors can be built to develop 450HP, and that's nothing to sneeze at.
Last but not least, the slightly smaller intake ports inherent to the SOHC heads will create more velocity of the intake air, so the SOHC heads will develop better low RPM torque than the DOHC heads, handy for duning. Many engine builders like the low end power advantage of the SOHC heads and opt for the trade-off, assuming 400-450+ HP is enough. "
-Quote from outback motors...
I still love my 98 DOHC
you can use jdm sti high lift cams (affordable)
and a nice shiny intake manifold http://www.outbackmotors.com/intake_manifold.htm