Yeah, this is probably meant to go in 'power adders', but, it doesn't bother me! Anyway, it's always going to be a compromise between boost and compression ratio. The more boost you have, the lower CR you need (obviously) or the more octane you'll need to keep from detonating. Now, you need to decide if you want to run 15 psi on pump gas. If so, you need to build your motor to suit pump gas. Basically you want as much CR as possible without detonating.
As far as actually lowering compression ratio, it's better to go with a larger chambered head/combustion chamber, instead of just getting dished pistons. This is because dished pistons have less material, and therefore makes the crown a little bit weaker. So, the best way to get the CR you want is with heads.
Now, you didn't mention what displacement your motor will be, but, i'm assuming stock disp. With a 346, a 72cc combustion chamber like the bigger chambered AFR's or LQ4/9 truck heads will get you about 9.5:1 on flat top pistons. Add a few CC's worth of valve reliefs in a set of forged pistons, and it'll drop even more, maybe 9.4:1 or so. I'm currently running 10psi on about 9.5:1 compression ratio, and the thing absolutely loves pump gas. No detonation problems at all, and it's been 90+ degrees everyday lately. I suspect that a similar CR would do quite nicely for you. You don't want to go too low on the CR, because that will affect spool-up and off-boost power on a turbo engine. I would think about 9:1 is as low as you'd want to go.
Hell, even stock Evo's have an 8.8:1 compression ratio, and can run 25psi or so on pump gas without too much of a problem.
Would it be easier on the engine if I upped the displacement, then went for high boost/low CR?
I was in fact looking for an LS6 based long block 383, 406 or even larger with forged internals and low CR, but couldn't find anything. Of course I'd like a C5R 427, but they're a bit too pricey, from what I've seen anyway.
It'd be easier on a bigger engine because you'll make more power on the same boost, or the same power on less boost. Pretty much, the more cubes the better, but even a 383 stroker short block is at least 50% more expensive than a stock displacement short block. It pretty much all depends on how much money you want to spend
I suggest you talk to one of our supporting vendors on the left. I went with a package from A&A and am running 10lbs of supercharged boost on a 9.5 to 1 CR forged motor. Im with BBaxR6, 9-9.5 to 1 is what you will need.