Probably 10th level, or 11th if you want to unlock a paragon path. Personally, I would go for E10; paragon feats are mandatory to catch up with the math, since +2 to attack and saves is significant in a way that a +1 isn't. Also, if you are getting only the initial bonus from a paragon path, some of them would be much stronger than others, so the thematic choice wouldn't hold.