Yep, throttle to 50%, all power to engines, flight assist off. Boosting will also speed up your turn rate but it soon comes with the increase in speed that lowers it, but if your opponent boosts past you, flick flight assist off and do a boost 180, you'll flip super quick and that speed will help catch them up. Don't forget to turn FA back on when you're done turning, unless you're super pro!
edit: Should also mention, it's not just 50% throttle, but 50% *speed*. If you're going max speed and you turn FA off to turn, it'll actually be slower than waiting to slow to 50% THEN turning FA off.