Having a lower compression engine doesn't enable you to run more boost in some way, it just takes more boost to make the same power as a "higher" compression engine at a lower boost level. The one limiting factor in an LS engine, in any application, will be the poor flowing characteristics of the head. Better flow is one determing factor in making more power. A b16b, has a cr of 10.8:1, where some would argue would be a little high for a turbo application. There are definitive advantages to each engine (b18b, b18c, b16), which would suit you best, depends on the specific application and your expectations for power output, or range and placement of power band.

Hope that helps.