Completely agree. I like the idea of a 6.4, but I think a 5.7 can do the job just as well, unless you are looking for the last couple of 10ths. And I like smaller V8's anyways.
Personally, I think the only real drawback to a 5.7 of any vintage is the cam. They are effectively a truck engine and stop pulling at 5200 rpm or so. My '15 R/T was a blast around town, but on the highway it felt strangled when I needed to pass and just wasn't as fun at the higher rpm's. The cam is too small, much like the 5.9's. So a 5.7 with a 6.1 or 6.4 cam and a better intake and exhaust if possible and I bet it would be hard to tell what's missing compared to a stock 6.4. There are probably better cams, but I like the OEM ones because they are cheap (or used to be) and the 6.4 cam keeps the VVT functionality.
My dream build is probably a forged Eagle 5.7 with AFR 212 heads (assuming they fit a 5.7 bore). Initial build would be with an 6.2 cam and later a HC blower since the AFR heads are dual drilled. No idea what kind of power it would make, but I bet it would be enough for me.
I like the idea of VVT and SRV as it makes the motor a little more of a "best of both worlds". But with a lighter car, maybe the "best of both..." ends up being too much on one end. :D
