assj and ussj are essentially the same only ussj just makes you even slower and thats why trunks lost to cell quicker than vegeta
it was clear surpassed 16, 17, and 18 during his training in thbtc but wasn't stated by how much plus he was still losing to the cell jr's who were only a little...
thats after piccolo trained in thbtc at full power goku mssj is 880,000,000 > piccolo 560,000,000
vegeta did use USSJ2 against semi perfect cell only the former was faster than the bio-android
USSJ muscles are big and slow the body down vegeta lost to cell because of them especially trunks whose USSJ 3 exceeded cell's power piccolo even stated it because trunks sacrificed speed for power in exchange
Goku MSSJ 50%: 440,000,000 > Vegeta Regular SSJ: 270,000,000 and Trunks SSJ: 195,500,000
his power is 800,000 after training with King Kai and it is 1,200,000 after he had fused with Nail (which is around Second Form Frieza's power level of about 1,000,000), it also states that his power is 2,000,000 during the Garlic Jr. Saga.