Kingston compatibility, problem with Voltages

Hello

I have a 2x 1GB Kingston PC8500 DDR2 1066mhz. Im now adding more memory(2x 2GB).

Problem is, I only found in stores the "new" pack with different heat-spreaders.

I should be getting this to guarantee 100% compatibility between my current memory and the new pack:
http://www.valueram.com/datasheets/KHX8500D2K2_4G.pdf

But I only found in stores this one.
http://www.valueram.com/datasheets [...] 1K2_4G.pdf

I compared both pdf's, and the only diference between both is the supose Voltage they need at 1066mhz. The normal kit says 2.2V, the kit with tunned heat-spreads says 2.2v, 2.3v.

Im no expert,but isnt there a small risk when I OC my 6GB to 1066mhz at 2.2v? since one of the packs MAY need 2.3v.

Or is complety safe? without heat-spreaders, memory packs are exactly the same. So if one works in 1066mhz at 2.2v,the other one should do the same. (check Pfd's please)

ty in advance