As you already noted, even a W-5 head struggles with a 4 inch stroke. I can make the argument that it isn't good enough (without massive work) to feed 345 inches at 8500.
We need to remember what these heads were designed for. The W-2 was designed for 330-340 inch engines, that were significantly induction limited. The W-5 head was an improvement on the W-2 and that's about all of that.
I've said before that a W-2 based engine, with today's cam and valve train with a reasonable RPM of say 7500 shift speed, with a well prepped head can only truly support 360, maybe 370 inches at that RPM. A single 4 hampers it even more, and required more total cam timing and will require more transmission gears with closer splits to keep the engine from falling too far below peak torque on gear changes.
With well prepped W-5 heads and the same configuration, my opinion is 385 inches or so is about all you can feed, relatively well.
That doesn't mean you can't use more inches. It will be down on specific power output, as in HP/CID and requires more cam timing, which obviously will start to peak the torque curve.
If you have enough gears, you can hobble the deal through.
That's my random thoughts on your question.
One last thought...if you use a 3.58 or even a 3.79 stroke crank I'd stick the longest rod in it I could. I'd rather use a 3.58 stroke and a 6.25 rod than be stuck with a 6.125 rod and a 3.79 stroke. When you become induction limited, rod ratio becomes more important.