At level 21 I killed a level 31 rogue with no problems. At level 25 I killed another 31 rogue, no problems. I'm sure at 28 I could kill a level 30 rogue with no problems.
I've only bought weapons for this character, the only other equipment I have is found or quest reward. I still have white gloves that are level 7 required. I don't plan on buying any new armor until level 40, when I can upgrade to mail.