Some other factors to consider:
3070s will require more rigs which increases the cost and makes more work to maintain them.
Older 4090s have a power issue with melting connectors, make sure the ones you're offered have the new connectors.
This is very good advice. The RTX 4090 video card is in great demand, and therefore is not kept in store warehouses. Now there are mostly new models on store shelves, but it is advisable to buy modern power supplies with connectors for these video cards for these video cards, so as not to use different adapters. With such power consumption, the adapter is the most dangerous place.