First, you picked the “luxury” motherboard chipset with more PCI lanes for the newer platform. The B650 is more comparable to B550. This is just an example of a B650 motherboard that has more than you’d need. Feel free to select a different one if it suits your needs better in terms of PCI slots and price.
So then the difference is $200
To answer your question: The newer CPU performs about 15% better in games, on average. Source
Is 15% CPU gaming performance worth $200?
Should I push for an increase in budget, or go with the 58?
The other reason to go with the newer platform is upgradability / future-proofing.
Mainly the next CPU generation (i.e. 9800X3D), but also in terms of USB slots, M.2 slots, etc. The B650 has more.
It’s too much to go over all the differences, but just comparing the storage (this is not on pcpartpicker, not in enough detail so I am, again, using tweakers.net as a source. Sorry, use Google Translate)
TUF B650 PLUS has
- 2x PCIe 4.0x4 M.2 slots
- 1x PCIe 5.0x4 M.2 slot
- 4x old SATA-600 connectors.
MSI B550-A has
- 1x PCIe 4.0x4 M.2
- 1x PCIe 3.0x4 M.2
- 6x old SATA-600.
You’ll see a similar picture in terms of USB connectors (backside and headers) and probably other stuff too.
IMO, this whole package is worth $200 unless you are building on a tight budget