For me the power of SIMT over SIMD is in its programming model. It becomes especially interesting for the more complex cases where you have data dependant branc

For me the power of SIMT over SIMD is in its programming model. It becomes especially interesting for the more complex cases where you have data dependant branching. No, it's not going to use the full power of your GPU anymore, but at least you can branch without restructuring your whole code as you'd have to in SIMD (and potentially make it less efficient when adding more memory accesses to avoid branching). Likewise, modelling the performance of a GPU kernel is quite easily doable compared to CPU. I found that roofline with some modifications creates quite predictable results. This is mainly because the memory model and the computational cores are all quite simple in comparison.