Yeah the big jobs can make some decent money, unfortunately it's just as easy to lose it sometimes, especially when a contractor does a bunk with £80k of your hard earned, but this year we are absolutely on fire, we have a couple of big jobs at £120k+ each running simultaneously, but the £3-10k jobs are were it's at right now for margins.
The big jobs are great and make big profits but usually spread over 6-12 months whereas we can usually get 10 x 10k jobs done in a month with higher margin % - to do so means needing more people to do it, manage it etc. It is however lower risk and usually better for cash flow.
I only mentioned the stress as we're growing rapidly again and haven't grown the management side just yet so it's rather busy. There doesn't appear to be as much skilled labour around anymore either, I read an article last week about a top London firm that were turning down £1 million of work a week because they couldn't get the staff for it. Crazy.