IPC is a metric, not a statistic. Your question is like asking what the miles per hour is on a Suburu WRX. The question does not make sense without some qualification (like max MPH) or other information (like what route is being taken, how much traffic there is, the road and weather conditions, who is driving, etc).
IPC is dependent not only on a large number of architectural and microarchitectural design decisions, but also on the software being run. The P4 and Athlon can both sustain 3 micro-ops per cycle (the Athlon has a higher fetch and dispatch rate, but they are both limited to 3 uops/cycle in issue, rename, and retire rate). You'll need to look at benchmark results to gain any sort of insight to what the typical relative IPC difference is between microprocessors (assuming the same instruction set and code path).