Selecting the Power rating of resistor
The power rating of a resistor is not the peak power (though that's in the datasheet too!) but the average power. So what you need to do is not only figure out the max power in a pulse, but also the duty cycle/ frequency of pulses. 

In your case, as an overestimate of the energy dissipated in a pulse, lets say that your pulse dissipates 4W for 4ms, so your total energy would be \$4W*.004s= .016J\$ (you can get a better estimate by having LTSpice integrate your power trace). Lets also say that these pulses occur 20 times/s, so you would need a resistor with at least \$0.16J*20Hz=0.32W\$, so a \$½W\$ resistor would probably be fine.