This is what I mean about the spike: http://graphs.headphone.com/graphCompare.php?graphType=7&graphID[]=573&scale=30 (link is bugged copy last bit)
Unless I'm reading this graph wrong I gonna need a amp that can drive headphones upto 600ohms to be safe.

Thank you.
 

You're not misinterpreting the graph's data but you are misunderstanding what it means.

All else equal, higher impedances are easier to drive well because they draw less current from the amplifier which results in less distortion.  In the real world all else is rarely equal though, and higher impedance headphones tend to have lower sensitivity than lower impedance models so you need to look at the efficiency specs to determine what amplifiers will be suitable for your needs.

Based on Tyll's measurements, the HD600s have a sensitivity of around 103dB/V (which is quite a bit higher than the 97dB/V that Senn themselves specify...) so, for example an output of 7.3 volts RMS (pretty much the O2's max on AC into higher impedance loads) will give you around 120db peaks which is plenty of head room.  I like the O2 just fine with my HD650s but other people around here will have different suggestions.  Pretty much anything they recommend is going to have enough voltage swing though.

That peak in the HD600's impedance become important when it's combined with the output impedance of the amplifier.  The higher the amp's output impedance, the more the peaks in the impedance will turn into EQ curves on the headphone's frequency response.  Something with a low output impedance like the O2 will make so noticeable change to the HD600's FR.  Something like a Bottlehead Crack with ~120 ohms of output impedance will give a few db of boot around 100Hz with the HD600.