It totally makes sense to use what you've got already. The only savings is -8 is cheaper for the fittings and hose than -10.
Like I said before, the -10 makes sense and works better for longer runs. Pressure and flow losses would occur if running oil to the front and back to the engine. You'd have about 20 feet of line to the front versus about 10 with the rear-mounted cooler.
I'm using -10 from the sump plate to the scavenge side of the 1st pump stage, and also feeding the pump from the tank to the pressure side of the 2nd pump stage. All my other lines are 8AN.
The only other thing I'll recommend is using sweep fittings where possible for 45 and 90 degrees. Don't use restrictive plumbing-type angles.