I've got a 7900 for a Graphic Design machine (picked one up around release date). Here's the highlights and pitfalls:
- Long boot times are true, but not horrendous. You get used to it.
- Excellent efficiency. I've seen very similar figures to the TPU tests (rarely going over 75W, 88W spikes, 55W average, regularly in the 40's)
- Pretty good at gaming, but other Zen 4 chips can best it for sure.
- Very strong application perf and perf per watt (why I bought it, helped along by a Gamer's Nexus review too). It crushes the design tasks I've given it.
- I've found the chip to run a little hot at idle, but the temps under load are pretty good (generally in the 50's and 60's with a 360mm CLC. Though, a more demanding game could push that up).
So, it's great, and I don't regret buying it at all, but a 7900X with Eco Mode 105W, or an upcoming 7800X3D will probably be the better option for anyone reading this.
But if you see a great deal on the 7900 a few months from now (especially if you need it for work), go for it!