My first Talon had door lowers, my second one does NOT. I rode down into the 30’s this winter, wearing tennis shoes and was comfortable. Note that not much air transfers, even with no lowers, the heat just hangs in the cab. My windshield also compounds the problem when it’s down, it’s almost always up, unless it raining or COLD.
Remove your hood and look at the chasm all the radiator heat is funneled into, the passenger ‘bucket’ keeps getting warmer as the day goes on, I cook like a lobster at anything above 80* outside air temperature. In a thread called Cab Dust (if I remember correctly) PaulF showed how he blocked off the tunnel opening, forcing radiator heat to exit past the tires instead of into the cab - he lives in Utah, so knows about heat.
The link in my sig has a link to some brackets that hold the doors open 3 or 4“ and they work well if you aren’t riding in tight woods, otherwise they’ll snag fer shur.