Ignition timing

In the seek of more top'end of this 250 with virtually non existent top'end comparing to the other 250 2-stroke i have ridden, i took a look on the ignition timing. Its set slightly before TDC maybe just 0.3mm, really hard to tell. Whats the common setting? I read on ericgorr's site that i should only change it 0.7mm thats very hard to see if i change it 0.5 or 1.0mm and as far as i can see how with the ignition wheel(dunno what its called in english) still mounted i cant see any max marks. Do you think i can gain much top'end by advancing it to TDC? How much effect does the ignition timing really have?