Put an OEM thermo back in it... Otherwise, deal with the low temps. Things like Nismo T-stats & larger radiators are made for running the car hard... Daily driving on them in the winter is going to yield low temps. You should be happy- If you were running a clutch fan, OEM shroud and cooling panel, your temps would likely be even lower.
You can also raise your coolant to water ratio... Less water + more antifreeze = less cooling. However, you would prolly be sorry come the GA summer
