Choosing the right carb for my car (340 4-speed)

Moving forward (not undermining the importance of timing, just progressing with the topic), do you guys think I should get the 650 DP ordered up and installed while I still have the option? I don't think the cost to upgrade from the 600 to the 650 will cost much, if anything at all.

All of the calculators that I have run have yielded a CFM range between 600 and 700. I have varied the V.E. between 0.8 and 0.9, and I limit the motor to 6,000-6,500 RPM. While I know the jets and power valves can be changed/adjusted, I don't want the carb to be a limiting factor down the line.

If you think the 600 will work fine, then I'm happy to just play with timing. I just need to figure this out while I still have the option to return the 600.

Thanks all.