CS by....

So I am new to LoL, I'm level 30 and have 2 champs left till I can start playing ranked games (not that I intend to straight away hence this thread.) As a new player I'm wondering what are good cs scores by certain points in the game? At 10 minutes with soraka (no masteries, no ad runes and no items) I had 60 cs, by 15 minutes I had 100 then at 20 minutes I had 150 and by 27 minutes I had 205. Now is this a good score? I know that in an actual match I would have to take into account the enemy champ, the other teams ganks etc (but I think that items and runes makes up for it to a degree). Now I know that some will say "It doesnt matter as long as you are above any team etc" but it does matter to me, its a skill that I feel I need and its one which is good to have. SOOO to get into say Gold or Silver league what should my cs realisticly be by 10, 15, 20 and 25 be? thanks in advance.