Look at the rpm that you are running when you are mudding. If it is higher than 3000 then go with the 185s. If it is lower than that go with the 165s.
Compression is where torque comes from and the larger heads are tuned to use a certain airflow - probably higher than a wheeler will ever see while off road. If you can find a cam that produces max torque at the rpm range that you use then that is the way to go. You aren't building a dragster and all that extra flow capacity on the 185 and 205 heads is just going to cause mixture problems for you below 2000 rpm in a stock engine.

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Paul
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retired mechanic after 35 years
specialized in Holley carbs and Ford Automatic Transmissions