2.15/1.67s look like they might be perfect for a 4.160 bore 428 though? i could see going bigger but there doesn't appear to be much more without the valves touching? I'll contact Andy's but it looks like they only sell certain sizes. If I go the Ferrea route is there a supplier you guy recommend?
With regards to the factory cast but not machined thermactor ports on these, I'm still not sure if they are solid or actually open on these castings.
I do think the 2.15/1.67 combo is good for a 428, but there are a few more options for undercut stem 2.09 valves compared to 2.09, so you can save a little dough. I do not think there would be a measurable difference in power, unless you had a very talented porter that can match the port to the slightly bigger valve.
Some things to think about, although guys all have their techniques, and porting is certainly not as simple as a cross section match, think about the port like a gradual funnel, reducing by about 1- 1.25% in size as it approaches the valve. If the port is matched to a 2.09, you won't gain much if any with a bigger valve. Add to that, you are probably starting from a med riser port location on the intake manifold, so high and "more square" as it enters the head, it's not like you want, or even can, use the whole low riser port in function.
2.09 or 2.15 really doesn't matter at your desired performance level IMHO, 2.15 is certainly a good enough option as is 2.09, but I'd consider thinking more about the entire intake port efficiency instead of maximizing valve size at your RPM. Valve design/shape, modern valve job (which not as many people do as they claim), bowl transition, bowl shape, size and guide area cleanup, width of the port, some work on the short side, transition at the roof of the intake at the carb, etc. The valve size is going to be a one small part of it (at your RPM/power level)
That being said, like Jay said, if you are going to go big, go big on the intake side.