Since he's a Super Saiyan 2, and based on his fights during this period, I'd say on Par with Super Saiyan 2 Gohan at the Cell games. Above is WRONG! Vegeta stated that Goku had more power than Gohan did when they fought cell, and Vegeta and Goku fought evenly, so since it's been 10 years at the end, and since Vegeta trains pretty hard, I'd say he could've reached, or at least been close to reaching super saiyan 3