Higher gear ratios put a heavier LOAD on the engine,.That load helps spool the turbo quicker. Low gears will also spool, but in 1st and 2nd you'll wrap through the RPMs faster than the boost builds.
P.S. There are VERY FEW N/A cars making the same HP as even a low-power turbocharged car.
1965 AC Cobra 427SC Replica [Carb Edelbrock 306ci SBF, 1980lbs]
2001 Mustang GT - [645WHP, 652TQ][MMR900 + Trick Flow Heads + Intake][ON3 Turbo @ 14psi]
2007 Jeep Grand Cherokee HEMI, 2006 Infiniti G35, 2012 Honda CRV EXL [The Daily Drivers!]