1. Performance & Speed Grade: The 71V65603S133BQI has an access time of 4.2 ns, corresponding to a maximum operating frequency of 133 MHz. In contrast, the 71V65703S85BQI features an access time of 8.5 ns, with a maximum operating frequency of approximately 117 MHz. The latter offers lower maximum data throughput during sustained read/write operations and cannot meet the high-bandwidth application scenarios designed for the former. 2. Timing Margin & System Stability: At the same system clock frequency, using a device with slower access time significantly reduces timing margin. If the original design operates close to 133 MHz, direct substitution may result in setup/hold time violations, leading to data errors or system failure. The feasibility of replacement entirely depends on the actual operating frequency of the target system and the timing margin available from the substitute device. 3. Cost & Power Considerations: Typically, a slower-speed device (71V65703S85BQI) offers potential advantages in manufacturing cost and dynamic power consumption. Such a replacement is often driven by the need to reduce BOM cost or optimize power usage, but inevitably comes at the expense of some performance.