Optimax?

[saxmund]

I filled up my recently purchased 156 2.0TS with ordinary unleaded, more or less on automatic pilot. I later looked in the manual, which said I should use petrol with more than 95 octane but I'm not sure what that means - I checked on a Shell petrol pump but it didn't seem to give an octane rating. So the alternatives are to continue with standard unleaded, use ordinary Super (which I'm led to believe are rarely worth the extra cost) or to use Optimax. What do the rest of you use? Do you get noticeable performance/economy benefits?