Yeah just let it do it's thing
If you find a 52x disc that'll only burn at 16x, disable it and see if you can burn faster without running into problems. That's why it's switchable, to allow for these kinds of anomalies (usually caused by the firmware not having the newest media in it's database).
Of course you should still be able to burn at slower speeds. So if the drive says 32x, you should still be able to select 16x. Personally I do this for music CDRs; select the fastest speed the drive will take without having to ramp the speed up over the course of the disc (which can have a negative effect on quality). Usually that means 16x or 24x.