Hello everyone
i'm in the same situation as our friend except i already have my I5 2500k. Currently i am thinking two options
1) Buy a HD6790 around 129EUR 
2) Buy a HD6670 70 EUR and a better CPU cooler 70 EUR and overclock the 2500k a little bit more.
The HTPC it's not intended for gaming. I use SVP MPC-HC and MadVr.
Bellow you can find a benchmark with the CPU at 4200 and cpu usage around 85-95%.
Test summary
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  Date: 2011-12-27T18:35:53
  CPU:  Intel Core i5-2500K @3300 MHz [4 threads]
  GPU:  Intel HD Graphics
  Mode: FHD + CPU [6 threads]
Overall scores
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  Synthetic CPU:                  MC2080
  Real-life:                      FC1693
Details: synthetic
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  CPU: compose (single-threaded): 644
  CPU: compose (multi-threaded):  2421
  CPU: search (single-threaded):  484
  CPU: search (multi-threaded):   1824
Details: real-life /FHD
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  decode video:                   13.37x (320.9 fps)
  48 fps - vectors search:        1.27x (61.0 fps)
  60 fps - frame composition:     1.35x (81.2 fps)
  48 fps - [SVP] fastest:         5.93x (284.4 fps)
  48 fps - [SVP] simple 1:        2.95x (141.7 fps)
  60 fps - [SVP] good:            1.32x (79.2 fps)
  60 fps - [SVP] high:            0.85x (51.0 fps)
  60 fps - [SVP] highest:         0.45x (27.2 fps)
  72 fps - [SVP] simple 2:        2.65x (190.9 fps)