Honestly, the best way to determine what works for you is to test, test, test.
I typically see higher impressions and clicks at the 1-3 position but not necessarily higher conversions. Unless the client requests otherwise, I'll try to stay around the #3 spot for high priority general words and in the 1-3 spots for branded keywords.
If I'm on a limited budget, I'll try to stay in the top 3 positions for my lower traffic, more relevant keywords and I'll drop my high traffic keywords to the 4-6 positions.
You have to also take into consideration that most searchers make multiple searches before they make a purchase. While your high traffic, general keywords might not show conversions they may be important in the first steps toward a purchase. As part of your testing, you may want to look at trends across your overall conversions when you try different position strategies for your general keywords.
If it is profitable with a 5K budget, the sensible thing to do would be to have an unlimited budget for keywords at that CPC but corporate budgeting processes still haven't always caught up to what is sensible to do.
