Since a high compression NA motor relies on vaccuum to pull air in it probably won't be such a great idea to aggressively port the heads. Unless your planning to rev really high.
The valvetrain loss argument between DOHC and SOHC heads is minimal because the SOHC heads still have rocker arms. Even though you have another cam to spin in the DOHC its touching the buckets.
Things to think about:
I upgraded the springs to supertech dual springs with titanium retainers because I plan to rev beyond 7000 and am going turbo. I also converted to a shim under bucket setup to keep from spitting shims at higher rpms. I would recommend a shimless bucket setup especially if your running high lift cams at higher then 7000rpms and turbo as well.
To be totally honest, try to find a set of DOHC WRX heads. In stock form the 04 and up came with shimless buckets and have a really nicely shaped combustion chamber. If you want to modify the heads you can easily find high performance cams and springs for $1000. On a side note if you ever need to adjust lash you will need to order the whole bucket ($25-each) since the shim is built into the bucket.