I built by playing lots and lots of $5 SnG's - many hands and slow and steady bankroll rise...

If you don't feel happy about playing a game where your stack is on the line but still wnat to play NL then you should either drop down in stakes or buy-in short and just play very tight (do a search for Miller short stack system).

Actually playing in short (say 50% stack) until you are comfortable with the apparent depth of full stacks isn't a bad idea and I still do it when I first move up.

I guess I didn't really make it clear, I seem to be able to play really well in tourneys and without tilt... I just find I get very stressed out in a cash game and tilt...

In a tourney it is like I have a set goal, make the money, then win it...

How much of a sample size do I need to know how well I will do long run in sit and go tourneys? - Because at the moment I only have 34 logged on my database (though I have played many more than that) and I make the money 73% of the time with 'ROI%' 114.61 ... I know these figures probably can't be maintained but If I could keep it above 50% I would be doing well?

Maybe I just need to improve my cash game so I have a clear tactic like I do in the sit & go tournaments?

Read and memorize Zen and The Art of Poker