Many years ago, Bruce Crower, did an article for one of the hotrod magazines, about what CR made the most HP. They used a VW engine, and did nothing but change pistons to drop the CR, and then cranked up the boostwith appropriate jetting), to once and for all answer, what CR made the most HP. He got down to 4.5:1, and was still making more HP. The problem at that stage, was just starting the motor....
Figuring out what CR suits you best is as much a personal item, as anything else. There are lots of people that have their own style of tuning, and can just get some combs to work out best for them....
Personally, I still think there's still alot on the table, code wise, for making a lower compression motor, more responsive, then what's currently *out there*. For awhile the aftermarket ecms continually talked about being easy to program, and while that's a good thing, it takes a fair amount of complexity to really optimise a tune. It's evident in the latest aftermarket offerings they're beginning to see the light about what's really needed. I'd wager, that in the next generation, of aftermarkets, they continue that trend.
Not to mention the converter makes a ton of difference, in how an engine initially spools up the turbo.
My 4.1L wound up at just under 9:1, instead of 7.5:1, and while it was almost like having a big block under the hood with a TA-62, I would perfered, the 7.5, just since there was no need for that much low end grunt.
Again, that's personal preference.