If you want to design for a maximum Ic of 5A then you do not want a 2N4401! That's a 0.6A transistor and I wouldn't sustain that for any length of time.
For these currents I'd recommend using a MOSFET instead, e.g., the Fairchild RFP30N06LE as a starting point.
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The Aussie Shield: breakout all 28 pins to quick-connect terminals