B670 is Intel, B650 is AMD. Did you by any chance mean the X670/E, which is AMD?
the higher level chipsets allow more PCIe lanes. But really, the only lanes you really need are to the GPU and the SSD. and both have direct connection to the CPU. They don't go through the chipset. anything going through the chipset, will be slower. that is where USB and secondary SSD go.
if you add a lot of extra cards, you have to look what limitations the MB has. Sometimes slots share PCIe lanes. but if it is only one SSD, and one GPU, it should not matter.
But look at the specific MB what it offers. Just because they use a chipset, doesn't mean they use all features. For higher power CPUs (especially if you enable PBO), the VRM (voltage regulators for CPU) design also matters. For specific MB etc., a computer forum may be better. Many people here will get a PC from the IT department, and there is not much choice. But on a computer forum, you have all the people that build their own PCs.
I don't know if Revit LT even offers all the rendering options. I think testing your current hardware rendering and then comparing how that hardware compares to proposed hardware would be a starting point. Revit performance is very personal and hard to benchmark. my project could be a shed with no electricity or HVAC or any colors, or it could be a World Trade Center with all type of renderings and and MEP systems.... it is the same software, but the hardware requirements will be different.
Gaming performance is easy to compare. You take a few game titles, you determine the resolution and Shader/RT settings and for everyone playing the game with the same hardware it will be the same experience. But in Revit, everyone is playing a totally different game in totally different levels of detail.
Revit version: R2025.4