My 1st 110 was a 2.5P i don't remember it being much quieter than my current 200tdi. (My tdi isn't that noisy, can listen to the radio or have a conversation easily at 70mph).
You'll certainly notice how much less power it has 83bhp vs 107bhp for defender 200tdi. and torque is down to 133lbf.ft from your tdi's 188lbf.ft. Part of the reason I sold mine was the engine was well worn and would struggle on steep hills never mind towing and even converted to lpg, 14mpg didn't make it cheap to run.