Que bom que deu certo!

Só pra termos certeza, coloca a saída do glxinfo | grep OpenGL

Só pra constar, essas temperaturas ainda estão bem altas

2015-02-15 15:23 GMT-03:00 ALBERTO VIEIRA FERREIRA MONTEIRO <albmont@centroin.com.br>:
Valeu, funcionou:

antes:
[root]# lshw -C display
  *-display UNCLAIMED
       description: VGA compatible controller
       product: Trinity [Radeon HD 7640G]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list
       configuration: latency=0
       resources: memory:e0000000-efffffff ioport:3000(size=256)
memory:f0300000-f033ffff

temperatura:
2015-02-15 13:02:01 temp1:        +90.0°C  (crit = +255.0°C)
temp1:        +90.6°C  (high = +70.0°C)
2015-02-15 13:12:01 temp1:        +93.0°C  (crit = +255.0°C)
temp1:        +94.2°C  (high = +70.0°C)
2015-02-15 13:22:01 temp1:        +91.0°C  (crit = +255.0°C)
temp1:        +90.5°C  (high = +70.0°C)
2015-02-15 13:32:01 temp1:        +94.0°C  (crit = +255.0°C)
temp1:        +93.2°C  (high = +70.0°C)
2015-02-15 13:42:01 temp1:        +92.0°C  (crit = +255.0°C)
temp1:        +93.5°C  (high = +70.0°C)
2015-02-15 13:52:01 temp1:        +93.0°C  (crit = +255.0°C)
temp1:        +91.5°C  (high = +70.0°C)

depois:
[root]# lshw -C display
  *-display
       description: VGA compatible controller
       product: Trinity [Radeon HD 7640G]
       vendor: Advanced Micro Devices, Inc. [AMD/ATI]
       physical id: 1
       bus info: pci@0000:00:01.0
       version: 00
       width: 32 bits
       clock: 33MHz
       capabilities: pm pciexpress msi vga_controller bus_master cap_list rom
       configuration: driver=radeon latency=0
       resources: irq:36 memory:e0000000-efffffff
ioport:3000(size=256) memory:f0300000-f033ffff

temperatura:
2015-02-15 14:52:01 temp1:        +79.0°C  (crit = +255.0°C)
temp1:        +79.1°C  (high = +70.0°C)
2015-02-15 15:02:01 temp1:        +81.0°C  (crit = +255.0°C)
temp1:        +80.4°C  (high = +70.0°C)
2015-02-15 15:22:02 temp1:        +72.0°C  (crit = +255.0°C)
temp1:        +71.0°C  (crit = +120.0°C, hyst = +90.0°C)
temp1:        +72.2°C  (high = +70.0°C)

[a hora do root está errada; ainda está no fuso GMT+3]