Hence the C in CSP.
Contemporary molten salt CSPs operate at ~700C, so the difference between the concentrator and ambient air temperature would be 3% (at 25C) and 6% (at 45C).
In other words, a 3% difference. Perhaps measurable at the output, but certainly not significant.
New CSP designs are coming along that are working around 1000C, which would render that delta even more negligible.
In contrast, while PV cells vary, I believe max power temperature coefficients of around 0.4% / 1C is a standard figure.
That means at 25C your panels are losing 10% of max capacity, but at 45C that number goes up to 25%.
A massive reduction in capability.
As an aside, your calculations are improper, even though results are close enough. 0℃ is merely 273.15K and the temperature at which water tends to freeze. E.g. PV efficiency is usually quoted at 25℃ (or 300K), so at -20℃ they could generate cca 120% of "max" (rated) capacity.
>improves magnificently with high temperatures
Thermal solar is a solar heat energy source + classic steam turbine. The efficiency of a thermal->electric converter (turbine) is largely governed by the difference between the hot and cold side.
Increasing both the hot and cold side temperatures equally would not increase efficiency, AFAIK it would actually decrease efficiency, and without lots of water, they can't use evaporative cooling either.