The Mark VIII is super cool. You don't see many of them on the road any more, at least not around here. The last one I saw was in Rochester, NY about 7 years ago, it was black and in really good shape.
I haven't decided yet. I'm pretty happy with my current shop and they've built some motors that were good, so I might go with them. But there are lots of shops out there and part of me just wants to buy a cosworth block and be done w/ it.
We'll see when/if it blows I suppose. This shop has had a few big turbo stock internals STis running around with between 400 and 500 hp for over 50,000 mi. .
Allegedly pistons are the most common failure point because the OEM ones are shit. I've considered doing headwork/pistons/cams etc but I think I'll just wait until this block starts to give and then go with new shortblock.
edit: I don't think i posted it yet in this thread. This car is ~350whp/~350wtq for the past 2000 miles. Heartbreaker mustang dyno reading, stock STi reads 215whp. Compression is still good... for now.