Ten Ga. wire is a better choice. The factory wire is sized for the average current and disregards the peak voltage drop of the "Pulsed" coil primary. So the average current is what the factory wire size is determined by, but the peak current losses are what needs to be limited for maximum performance. Keeping in mind the average current in the wire is determined by RPM's and the peak current is always determined by wire resistance and the dielectric resistance of the compressed fuel/air mixture.
The voltage drop across the wire during the "Pulse" is calculated by peak current x peak current x wire resistance. The peak current losses (Voltage drop) will be the same every current pulse but the average losses (Voltage drop) will increase with RPM's.
minimizing the wire length and resistance (Thicker wire/smaller Ga.) from the HEI to the coil primary will give you the strongest spark. The thicker Ga. wire has lower resistance and becomes more critical as the compression of the motor increases. The higher the engine compression the greater the "Dielectric resistance" of the fuel/air mixture becomes... so a smaller gap at the plugs and increased wire Ga. and minimum required wire length becomes more significant... Higher the compression the higher the dielectric resistance and the smaller the gap should be.
If you use crimp lugs I recommend "Tinning" the wire with a soldering iron prior to crimping, then after crimping the tinned wire in the lug, solder the crimped wire to the crimped lug. The slow effects of corrosion will take it's toll in time, increasing the voltage drop as the inevitable oxidation occurs. So, the normal (Untinned) wire to crimp lug connection, in time, will exceed the wire resistance losses and slowly degrade the spark. Also, when tinning the wire, make the solder go to the heat, place the solder iron on the tip of the wire and place the solder near the insulation and the solder will wick towards the iron and wont migrate under the insulation of the wire.