Oh wow, dont listen to the machine shop guy. Prime example on this board: Darshu, blew his 98 RS head gasket @ 4 PSI.
The problem is that Subaru NA head gaskets are natorious for blowing and not staying in, even when NOT underboost. It has become such a problem that subaru has had to redesign their head gasket to the new 4 layer one, however, this does not necessarily make it better for boost. If you have the heads off, spend the money on the o-ring job, because it will save you time and money in the long run. Also, you wont have to worry about the head gasket being the weakest link.
BTW... they are compatible. If Im not mistaken, the new head gasket has metal rings in it that confuses people because it looks like it itself is an o-ring. No, this is just part of Subaru's new design. The o-ring actually goes outside of the perimiter of that metal piece to provide an extra pinch.
Here is a pic
This cost me 80 dollars, Darshu paid 140 for his job... depends totally on the machinist. BTW, some peope use Copper wire, other's use mechanice wire. I used mechanics wire because it is less likely to get marred when putting it in, like copper.