Cellular vehicle to everything (C-V2X) communications is presented as the cornerstone for next-generation connected vehicles. C-V2X can support efficient vehicle to vehicle and vehicle to infrastructure data transmission, and is said to be a key enabler of cooperative connected and automated mobility (CCAM). Performance of 5G New Radio (5G-NR) is expected to address bandwidth and delay requirements of services for autonomous vehicles. This is the theory and what particular research works have showed through simulation or limited prototypes. On the contrary, this work focuses on evaluating real 5G deployments (including 5G-NR) of network operators in CCAM scenarios, with particular emphasis on cross-border settings and service continuity under inter-operator handovers. The paper presents an evaluation platform to gather cross-layer measurements, homogenise results, perform comparative assessment of figures of merit, and calculate network and CCAM key performance indicators (KPIs). The platform is evaluated through implementing a use case for autonomous overtaking, involving two 5G-NR operator deployments at the Spanish-Portuguese border. Results reveal good network performances and correct operation of the service, thanks to 5G-NR and edge servers, although significant impact of handovers is detected on network and overtaking KPIs.