Fagerson played for 50 minutes in his first game for five months since suffering a broken ankle while Turner lasted 71 minutes on his return from an ankle injury, with both players now in Six Nations contention.
Speaking to BBC Scotland, Rennie said: "George was phenomenal, his throwing was excellent, he was great with the ball in hand.
"It's obviously great to have those guys back. We will see what (Scotland head coach) Gregor (Townsend)'s plans are. We've got a fair chunk of guys going up to camp to start preparing for France."
Scotland are aiming for a first victory in Paris for 20 years on Saturday when their Six Nations campaign resumes after an opening win over Italy and a defeat by Ireland.
With first-choice tight-head Willem Nel struggling with a calf injury, Fagerson's return could be timely, with the inexperienced D'arcy Rae backing up Simon Berghan against Ireland.
Turner's return adds depth to Townsend's hooking resources, with Glasgow team-mate Fraser Brown already back in harness, coming off the bench to replace Stuart McInally against Ireland.
"I thought Nick had a really big game, really strong defensively, got a lot of ball in his hand and he played a big part in the first two or three tries," Rennie said. "The little man had a good shift."