I think that finally getting control over your 660M is not that easy, mostly because of power plan related tricks.
Here's a small guide for you, it should address questions you just had, including the ones from yuvrajgill10, myhalfsoul and shou. Step by step:
1. Install nvidia 304.79 beta driver using 'clean install' option (available in custom install). Not abolutely required, but I have found these driver to better handle the profiles and less situations where apps used integrated Inter graphics instead if 660M
2. Set 'dynamic levono graphics' power plan using lenovo energy app (this is very important, as only this power plan gives you control over GPU and memory clocks, lower power plans let you control just memory clock. However, if you only want to fix the 'lenovo bug' and do not want to overclock later, you can continue skipping points 2-3.
3. Let's check if power plan just selected works ok and 660M enter boost mode:
4. Start GPU-Z
5. Select 660M in the selector on the bottom
6. Click the question mark close to the 'bus interface' and then 'start render test' - you should see a new window with animated blob. If 'lenovo bug' affect your laptop, already this test can show some colorful flashing apart of slowly moving blob.
7. Now let's check the clocks. Do not close the render window with the blob, in the main GPU-Z window select sensors tab, again select 660M on the bottom. You should see now the current clocks of your 660M. At this point, if power plan is selected properly you should see 950MHz on the GPU Core and 2500 on GPU memory. If you see like 835/2500 or anything else your power plan is not ok. Try to restore default settings using power settings in windows control panel, eventually reinstall lenovo power management application.
8. Let's play with the clocks. Close GPU-Z, install MSI afterburner, restart. No special Afterburner settings needed.
9. In the main Afterburner there are several sliders for voltage and clock adjustment.
Afterburner's settings are relative to the 660M default settings, so to decrease you need to enter negative value. I have set memory clock to -50, so I should have 2500-50=2450. Do NOT close Afterburner, just minimize when you're done with it.
10. Let's check if new clock is ok. Repeat steps 4-7. You should see the value just calculated reported as being used. If render test is still flashing, decrease memory clock a little bit more.
11. If you want to overclock the 660M GPU core you can change also the core clock now. I have set core clock to +135, so the expected clock is 950+135=1085 for core (remember, starting value is 950MHz from boost, if you did not enter boost in point 7 this adjustment will not work!)
12. Try some games/benchmarks for stability. If ok, you can let Afterburner start with windows an apply your clocks at boot. At the same time you can forget having 'lenovo bug'.
Hope that can help everybody having issues on the Y580 graphics or just willing to get some more performance from their rig..
@myhalfsoul: I would appreciate if you could do the check on your replacement laptop using steps 4-7 from this guide noting memory clock value and additionally read the BIOS version from main GPU-Z window. I am really interested how the issue is being solved by lenovo 
BR,
Chris
