Winch Extension question

[Antichrist]

If you put a 5/16" synthetic up against a 5/16" steel line, the synthetic will have almost 5000lbs + greater breaking strength (assuming standard Amsteel Blue vs a 7x19 aircraft cable). I'll take the greater breaking strength any day, not to mention the reduced mass.

As I've said in other threads, I've seen and read of synthetic breaking a lot more often than wire rope. Whether it's over loaded, mishandled or defective doesn't matter, a break is a break.
So based on that, IMO, you're more likely to have wire rope flying around if you mix the two.
Aside from that, I can't imagine any reason why it would be bad to mix the two, or that it would in fact matter which was the winch rope and which was the extension.