The difference would be minimal no?
We have no idea! There are some scattered benchmarks online saying the Tiger Lake CPU offers minimal improvement over Ice Lake, IPC boost of 2-4%, Intel doomed, etc. There's also a lot of reason to speculate those benchmarks aren't reliable, especially because Intel has been screwing around with configurable TDPs for their chips, it's hard to get a comparison between any two of their chips in like-kind thermal settings. But let's pretend they are all true--I'd
still wait.
The iGPU in Tiger Lake still has 96 EUs (Intel's name for groups of shader cores) compared to 64 in Ice Lake. On the face of things, this is a
lot more graphics performance. Shader cores and graphics performance are like the closest thing in the world to linear scaling; Intel is basically promising a 50% boost here. Now it could be smoke and mirrors. Maybe Intel reconfigured the EUs to have less shader cores per group or something. But personally, if I'm buying a machine where the iGPU is the main GPU, I'd be willing to settle for a fraction of Intel's promised performance boost.
Tiger Lake could also support LPDDR5 and PCIe 4.0. These are both a "maybe." We could get one or both or neither, but either one would be a nice plus.
So there are a huge range of possible outcomes here.