I emailed Darius @ CP Pistons at length, and he presented me with quite a few options. I couldn't believe how many different ring combinations they had available!!! Coupled with custom compression ratio, and CP Groove, and lateral gas porting, I had my hands full with choosing the right custom piston for me.
But although lateral gas porting helps achieve a greater ring seal, apparently the ports can fill up with deposits and reduce the efficiency of the porting, and are more suited for race applications where engines are pulled down and rebuilt every few races.
But the off-the-shelf piston, comes with the CP Groove, and raises compression from 8.6:1 to about 8.8:1... Coupled with decking the block/head (increasing compression slightly) and 1.2mm head gasket (lowering compression slightly), I should end up with a net compressoin ratio of about 8.9-9:1 which sounds perfect.
I'm really against dropping the compression ratio to facilitate using higher boost.