If you disassemble the factory binaries, you'd discover why the car "feels" better with a lower temperature thermostat. The factory fuel map adds fuel at temperatures below the design point. Here is an example of some factory parameters related to coolant temperature:
Closed-Loop Operation Parameters
CTS < 14.7ºC (58ºF) for 75 seconds;
CTS >14.7º (58ºF) and < 40.7º (105ºF) for 51.4 seconds;
CTS >40.7ºC (105ºF) for 12.5 seconds;
O2 >0.699V & O2<1.99V for 10 seconds;
Coolant Temperature Sensor Related Parameters
BLM enabled between 50ºC (122ºF) and 140ºC (284ºF)
Cold spark advance disabled above 56ºC (133ºF)
Hot spark retard begins above 116ºC (240ºF)
Highway Mode spark advance > 59.8ºC (140ºF)
Knock sensor disabled below 66.5ºC (152ºF)
Power enrichment at base A/F ratios > 56ºC (133ºF)
Target IAC idle RPM >80ºC (176ºF)
IAC multiplier at 1.0 (base) > 32ºC (90ºF)
Knock Control enabled > 67ºC (153ºF)
EGR Duty-cycle enabled at 56ºC (133ºF)
EGR Duty-cycle at MAX >80ºC (176ºF)
TCC lockup enabled >50ºC (122ºF)
SHIFT light enabled >50ºC (122ºF)
Diagnostic communication enabled at 70ºC (157ºF)
DTC 43 enabled > 90ºC (194ºF)
Cooling fan #1 enabled at 107ºC (226ºF)
Cooling fan #1 off at 104.7ºC (220.5ºF)
Cooling fan #2 enabled at 115.2ºC (239.5ºF)
Cooling fan #2 off at 110ºC (230ºF)
Cooling fan duty cycle at 100% at 80ºC (176ºF)
Acceleration enrichment multiplier at 1.00 below 80º C (176ºF)
Acceleration enrichment multiplier at 0.75 above 80º C (176ºF)
Acceleration enrichment multiplier at 0.50 above 104ºC (220ºF)
Acceleration enrichment decay factor at 25% below 80º C (176ºF)
Acceleration enrichment decay factor at 40% above 80º C (176ºF)
Acceleration enrichment decay factor at 50% above 104º C (220ºF)
Acceleration enrichment decay factor at 60% above 128º C (262ºF)
Fuel limiting factor timer at 217 counts below 80º C (176ºF)
Fuel limiting factor timer at 169 counts above 80º C (176ºF)
Code 13 (oxygen sensor fault) enabled above 70ºC (157ºF)
Code 14 (CTS high fault) enabled above 130ºC (266ºF)
Code 32 (EGR fault) enabled above 30.5ºC (87ºF)
EVAP canister purge enabled above 70.3ºC (158.5ºF)
Hot closed-loop timer enabled above 70.3ºC (158.5ºF)
Rich/Lean O2 offset at 16 counts between 20ºC (68ºF) and 92ºC (197.5ºF)
A/C clutch disabled above 150ºC (302ºF)
Miscellaneous
25.3º maximum allowable knock retard when not in WOT
As you can see, many of the operating parameters depend upon the coolant reaching 176ºF. Particularly interesting is the acceleration enrichment, which starts to fall off above 220ºF. That curve alone, along with the injector PW versus CS is why the engine "feels" better at lower coolant temperatures. It also wastes fuel and doesn't burn as cleanly.
If you take a lesson from NASCAR crews, you'd run the coolant around 235-240ºF, just like they do. That gets the peak power (and therefore, mileage) out of every drop of fuel. They are restricted in displacement, valve lift, and often in throttle bore size, so they have to make the most power from what they are given. That's why they run the temps higher. The factory has been doing this for at least 20 years. Thermodynamics don't take a rest and don't cut any breaks for people who don't understand them. They apply no matter if the car is a 120HP grocery getter or 850 HP normally aspirated race engine.
If you want to go further, you can enable the factory Highway Fuel and Spark modes at cruise. This programming has been included in factory binaries since the '80s, but never enabled because it might affect how the car reacts on the emissions treadmill (too lean means too much NOx) and potentially risks warranty coverage. If you car is out of warranty, and you don;t need to meet emissions requirements, you can enable the HFSM and get over 30 MPG with a 1980s V-8. If your cat converter is robust enough and the EGR is working properly, you'll still meet emissions standards. I can point you to several documented examples of where this has been done with success, including my programming and others'.