What is the benefit of an added internal metal frame/core on vinyl windows?
We are about to replace our 1965, single pane, full metal jacket, rattle-when-a-helicopter-flies-by windows. Since we want to get rid of the metal frame and trim we need to do a full replacement of the entire window, including the frame.
We have received quotes for windows where the frame is made entirely of only vinyl; a cut-away of such a frame is shown below:
Another (more expensive) quote had windows that included an internal metal frame, sample shown below:
I have been cautioned against windows that are vinyl-only as they may be more susceptible to thermal expansion and contraction, especially since we are in Southern California. Additionally, above a certain size, vinyl-only windows supposedly are more prone to having the frame sag over time.
We do not live in a "fancy" neighborhood, so vinyl windows are appropriate. However, I wonder whether going with a high-quality vinyl-only window is sufficient or whether a metal frame is more desirable for long-term survivability of the investment?