These guys have forgot more than I'LL ever know but don't try to figure CR without an actual measurement. A 'dial on a bridge' is the most acurate practical way to measure how far the piston is up but at least use the filler gage as suggested or buy a dial caliper if you can and make several checks around the piston should get you close.
If you have 8.4 DCR you are in good shape with hi octane and DCR is actually considered a measurement of detonation resistance. As suggested,do a cylinder pressure check.
Some guys are running well over 220 psi but if you follow the suggestion Denny gave you should be safe,,,,considering this is a street driven vehicle.
And as stated,cam intake closing point does have an effect on how the motor will tolerate compression ratios because it doesn't start untill the valve closes.