The SPCR test of Grand Kama Cross shows the temperature increase of 38 to 49 degC. So the core could be damaged?
IMO absolutely no: those temps are not comparable to your one, they are referred to Nehalem CPUs (Tjmax 99-100°C), and if you look at the charts, the Mugen 2 has similar temp rise (39°C to 45°C).
Moreover, if your X6 is supposed (by AMD) to work flawlessly using the crappy stock cooler
, how could such a much more massive Grand Kama Cross reasonably fail?
But you may do your own testing: load the cores with 5 instances of Prime95, start FurMark to have an heat build up by your graphics, how much is the current temp rise? Add the presumable summer edge, and you'll have your estimated max temps: worse than it, a Grand Kama Cross cannot perform (at its max noise level).
Broadly speaking C3 Phenom II X4 (Zosma) and Phenom II X6 (Thuban) are very cold CPU, and AMD has accustomed us that their more recent K10 CPUs work with a lower temp rise than Intel coeval counterparts (Wolfdale/Yorkfield/Clarkdale/Lynnfield), despite the higher actual power consumption (see the recent 80W 565 SPCR review for a dual-core comparison).
These are the arguments for the rationale abstract: while, about feelings, if you feel more comfortable with a 4°C edge at 680rpm, well, go for what you may like more. IMO it's about useless.