Stimson's side, who are currently 11th in League One, host the Lions on Saturday before League One encounters against the other 'big three'.
"I can't wait. If I wanted a comfortable life then I'd have stayed at Stevenage and just enjoyed that level of football," he told BBC Radio Kent.
"But I wanted the buzz of playing Leeds and Millwall, and now the likes of Charlton and Southampton to test myself and test the players we've got here.
"They are the games that are going to test us mentally as well as physically. So I can't wait for it to come around.
"No disrespect to the teams we've played, because we've played some decent sides. But it's the proper football now isn't it. They are the games that are going to test us mentally as well as physically."