Is there some kind of lookup sheet or something similar that can give an indication of how many points you get for onsigthing / flash / toprope / redpointing a route?
"It would be nice to work out what grade route I should onsight / what grade route I could redpoint to improve my score..." Luckily its all about the points mate! But to answer your question: Climb harder then what your top 10 shows, so looking at your card, ur best is a 5c and you got some 5b and 5a there as well. Climb harder then a 5a and you will get more points for you card.
There used to be a link on the bottom right side of the main page which tells you how many points for which grade and which style you get. But that link doesn't work me for right now. Here is it anyways: http://www.8a.nu/cgi-bin/scorecard/login.cgi?langue=ENG
How does the scoring work?