|I've never heard of a modern 4500 rpm hard drive - that should probably be 5400 rpm.|
All other things being equal, the 7200 rpm drive has a higher max continuous data transfer rate.
You could compare the max continuous data transfer rate of the specs of two models to see what the actual difference is with all things taken into consideration.
The max burst data transfer rate - e.g. UDMA 100 - 100 mbytes / sec - can only be maintained for short periods of time, the amount of time depending on the size of the memory cache on the drive's board
You won't notice the difference for smaller files but you will notice a slight difference for larger ones.