Zen 3 is ahead of Tiger Lake by ~6% in IPC. Rocket Lake is supposedly lower IPC than Tiger Lake so it has to be clocked significantly higher on 14nm to beat Zen3, which is unlikely. Zen 2's weakness in gaming was primarily due to the split L3 cache and that's been fixed in Zen 3. Intel isn't doing anything groundbreaking in Rocket Lake so I don't expect anywhere near 20% in gaming. I see Rocket Lake either matching Zen 3, or slightly ahead at best (at much higher power consumption).
6% ahead in what though? Zen 3 is miles ahead of Comet Lake in most workloads but still only marginally ahead in gaming. And the rumours suggest that Rocket Lake will have at least a 15% IPC uplift over Comet Lake + equal or higher clocks (5.3-5.5Ghz boost) with a specific performance focus on gaming. If true then my take on that would be that RL might trade blows with Zen 3 in the 8-core segment for non-gaming apps but take a fairly significant lead in gaming. The caveat being that it's limited to 8 cores. Would I still prefer a 12 or 16 core CPU for gaming even if in today's games it's say up to 10 or even 15% slower than Intels fastest 8 core Rocket Lake? Most likely yes.