Hi Syracusa,
If is was me I would vote for the courser wool (the Shropshire) because according to most of the woolen mills I have talked with a courser breed makes a more suitable and more resilient material for a topper (vs a comforter) than the finer breeds (see post #6 here). The fact that it can be washed would be an additional benefit.
A 1/2" wool topper or mattress pad and often even thinner can make a significant difference for most people in terms of sleeping temperature but thicker layers of wool would have a different feel and you would “feel” more of the properties and firmness/softness of the wool and less of the latex underneath it. Depending on the firmness of the latex and the specifics of the wool topper this could feel softer or firmer but either way it would feel “different” from latex. Post #1 here which includes some good comments about the effects of a thicker wool topper would also be worth reading.
Phoenix