I'd go with the flat tops and the smaller chambers.
I know you want the lower compression ratio, so use the fact that you want a given ratio to your advantage.
Working the heads to unshroud the valves will be an advance to your engine's ability to produce power!
Having those 64cc chambers worked by a professional (a good one, not just anyone) will increase the cylinder head CC, dropping compression down to where abouts you want it, and the Worked chambers will produce more power then the big unworked chambers.
Something to think about.
Dont just aim at a compression ratio ethier, becuase you'll try and cut compression by running more piston to head clearance, get optimal piston to head clearance then work from there.
Destroying the "squish" between the piston and head will produce more chance of detonation, even with lower compression.
Squish is essential to producing turbulance in the air/fuel mixture.
Our Goal afterall is making power
David Vizard is big on mimizing comression ratios, but being focused on optimizing power. Building something in a particular way that may make less compression, but makes enough "extra" power to offset the compression loss, then its a better way to build the engine.
Having less surface area in the combustion chamber is how to keep the power in the cylinder, becuase the more of the flame front the touches the chamber and piston, the more power will be lost to heat transfer through the cylinder heads and piston tops, as well as the cylinder walls as the piston travels down (but you cant help that).
So my personal perspective on things is to build with a given compression ratio "in mind" but try to achieve it with the least surface area touching the flame, optimized "squish", and a well worked chamber.
This will minimize chance of detonation, and therefore allow you to use lower octane gas, which makes more power becuase it burns faster.