His decision to opt for Bolton disappointed Birmingham who also matched Aston Villa's asking price, believed to be £5million.
He said: "Obviously it is not ideal moving across town to play for another club. But it would not have bothered me that much. As a player you have to do what is right.
"If I felt it was the right move, I would have gone to Birmingham but I thought Bolton was the correct path to take. It was a hard decision to move away from the midlands as I had been at Villa since I was 13."
Although Gary Megson's side are only two points clear of the relegation zone they are still in the UEFA Cup and face Atletico Madrid over two legs next month.
The prospect of European football, however brief, appeals to Cahill.
He said: "There is a lot of quality at this club. You do not get into the UEFA Cup with average players. It is brilliant to be at this level as you want to be competing with the top players. You get an indication then of where you are at in your career."