Since you aren't planning to have a refrigeraton loop (the normal geothermal heat pump arrangement) the best you can hope for is an approach (differential) to ground temperature. Fin efficiencies aren't all that great and I doubt you will want to use a high volume air source--further depressing the heat transfer coefficient. Plus this will be primarily a non-condensing mode. Condensation can increase heat transfer coefficients, but without refrigeration or a particularly cold source, this is an unlikely mode for the operation of your loop. Jim's comments about the length also are relevant as a cap--since the heat must be conducted away through the soil as source. The input power of the pump also comes into play, but I assume the pump would be before the ground coil so it's heat would be dissipated to the ground. (A monster pump would be a bad idea. I suspect a powerful fan/blower would also be bad as they might introduce more heat than can be removed or at least exceed the point of diminishing returns for their energy input.)
To put it in easier to understand terms: don't expect much. It should give some cooling due to temperature differential. It will not give you any dehumidification. That might be all that you require, but I suspect that some dehumidification is what you really need in Summer in Ohio.