AMD Ryzen 5 7640HS's Advantages
Better graphics card performance
Higher specification of memory (LPDDR5x-7500 vs DDR5-5200)
Larger memory bandwidth (89.6GB/s vs 83.2GB/s)
Higher base frequency (4.3GHz vs 4.0GHz)
Lower TDP (35W vs 45W)
AMD Ryzen 5 7645HX's Advantages
Newer PCIe version (5.0 vs 4.0)
Larger L3 cache size (32MB vs 16MB)