I tried tu pull 5 kg verticaly with a stepper: 15V, 0.4A, 100mNm and a gearhead 2:25. I calculated: 0.1Nm*12.5*72(gearhead efficiency) / 100 = 0.9 Nm So, shouln't it be possible to pull 5 Kg with a 1cm wheel?
Be aware that stepper motors are rated by holding torque, not quite the same as pulling torque, but probably close. Also the torque rapidly drops off with speed.
But the ultimate test is trying it! If you can use a smaller wheel if necessary then its not too critical - change to a smaller wheel until it can pull the load.