Assuming Pietro has full control of the Power Gem, all of his stats would increase to the point that he would be impossible to beat. Team loses badly, if written properly.
1. Pietro's speed is a strength feat unlike The Flash.
2. The Power Gem should in theory increase not only his strength, but his speed if he had mastery over the Gem.
3. Many writers have left out the fact that the Power Gem was written to make its user physically invincible. I'm assuming that this was to make for good stories, because let's face it, who would be able to oppose a Gem wielder on a physical front, if they were impossible to beat.
4. In a comic I can see the team having a hard time beating him, but in a forum match with PIS barred, this is likely a literal stomp for Quicksilver.