Large wind turbine blade bearings require reliable sealing systems to retain lubricants and prevent contamination throughout their service life. Seal performance is strongly influenced by relative movements of the bearing rings and by internal grease pressure. This study investigates ring deformations and internal grease pressure in a grease-lubricated 5 m three-row roller blade bearing using the Fraunhofer IWES BEAT6.1 test rig. Bearing ring movements are assessed using a validated finite-element model that includes the bearings and adjacent support structures that emulate blade and hub stiffness properties. Internal grease pressure is measured experimentally under representative operating conditions and under extreme scenarios involving closed grease outlets. The simulations predict maximum radial gap variations between -0.29 mm and +0.59 mm and maximum axial displacements of up to 0.41 mm, remaining well below the sealing system's allowable movement range of ±1.5 mm. Pressure measurements show no significant pressure increase during normal operation, while extreme conditions with blocked grease outlets and no pitch motion result in pressures up to 2 bar. Introducing pitch movement rapidly reduces pressure levels to below 0.5 bar. The results demonstrate that the investigated sealing concept is capable of accommodating the expected ring deformations and pressure levels of a large three-row roller blade bearing. Furthermore, the study provides experimentally validated boundary conditions for the design and assessment of sealing systems in future wind turbine blade bearings.