I fly the Pacific more than the Atlantic (first NAT track in over 2 years was last week!). However, I have seen winds to 220 knots over japan and the western Pacific. The jet stream max typically may be anywhere from FL330 to 370.
It is common to experience turbulence (officially "light" to "moderate" most times, but feels like "severe" to the SLF) when near the jet stream, especially when crossing it perpendicularly. Often, once established within the core of the jet, the ride is smooth. A lot depends on the wind shear (variation of wind with altitude) at/near your current FL.