Nominally 645 GB/s versus 800. The cache layout also shifts. I don’t know of a good comparative LLM benches between the two but AMD’s put out some first party numbers comparing to the 7900 GRE, which gives an idea. Absent reason to expect regular use of 16-20 GB GDDR, personally I’d bet on the 9070 XT.
And probably not even then. 4x16 offers 31 GB/s bandwidth while 5x16 is 63 GB/s. So, unless there’s a high end drive array, a very optimized loading stack, and DDR4-4000+ or DDR5-5600+, PEG isn’t going to be the bottleneck on dual channel DDR. We have a whole thread about how LLM loading speeds tend to get stuck around 2 GB/s.
If it’s transfer of cached coefficients from high overclock DDR4 to GDDR then PEG’s a potential bottleneck. But I don’t know of any data showing it’d actually be hardware limited rather than thread bound in torch or whatever. If it is hardware constrained I’d expect DDR5 to make more of a difference than 5x16 PEG.