What is correct idle in gear?

[The Plastic Lizard]

So I am tuning up the 84 crossfire tomorrow. Have seen conflicting information on the correct idle speed. What is it supposed to be in drive with foot on brake and in park?
Thanks

[terry82]

my 82 runs about 650 rpm when warm in gear .

[TigerDriver21]

I had a restored '85 C4 Corvette that when idled, would hover around 600-640 rpm, but there were not any adverse effects from that.

[crossfire1982]

My 82 idles warm in gear at 650