A semi-closed system running at 15 psi- an extremely common passenger car over-pressure- has a boil over temp of 247*F
It would shock me almost to a literal early death if cheapskate GM used a different psi rating.
My original '07 GXP ran from 200-215*F normally in the summer. My present '08 GXP just ran 195-204*F at 55* F outside temp in moderate stop and go traffic. No worries from my quarter.
Driving and working on a Sly 2008 Solstice GXP 5spd 260/260, and the worst-built 2012 LS3 Camaro 1SS to escape from Oshawa.
Gone but not forgotten:
2007 Solstice GXP 5 speed 290/340
Stored and needing to part ways with a 1970 Skylark Custom convertible I have owned since 1989 and turned into a GS455 clone. 462 with 7/8 primary headers, adjustable roller rockers, TA Performance Stage 1 aluminum heads, auto, Chevy 12 bolt, 3.31:1. Sadly a project car now but a driver from '89 to '06.