6G Internet of Things (IoT) systems will support massive deployments of energy-constrained devices operating over long lifetimes, with sustainable and reliable communication being a key target. Proper design of future IoT is expected to rely on an in-depth understanding of existing cellular IoT (CIoT) deployments, currently based on Long-Term Evolution Machine Type Communication (LTE-M) and Narrowband-IoT (NB-IoT) technologies. However, the impact of operator configuration decisions on device energy-efficiency and quality of service (e.g., transmission latency) remains under-explored and is rarely analyzed across deployments. This paper presents a measurement-based analysis of energy consumption and latency in commercial CIoT deployments across the Nordic countries. Using controlled laboratory measurements, we evaluate Radio Resource Control (RRC) connected-state duration, connected-state energy consumption, and application-layer round-trip time (RTT) under different radio conditions. The results indicate that operator-specific configurations have a key impact on performance differences across LTE-M networks. In particular, short RRC  inactivity timers reduce energy consumption by shortening connected-state durations. Additionally, activating the Connected-state Discontinuous Reception (cDRX) improves efficiency during longer connections. In contrast, when cDRX is disabled, energy consumption increases despite similar connection times. For NB-IoT, working in poor radio conditions (i.e., adopting higher coverage enhancement levels) significantly increases connected-state duration, energy consumption, and latency. Overall, LTE-M provides lower energy consumption and latency, whereas NB-IoT extends coverage at the cost of higher delay and energy use. These findings show that operator configurations are a dominant factor for IoT deployment effectiveness and suggest that adaptive configuration mechanisms are important for improving the efficiency and performance of future CIoT systems.