If you're needle is just under the 80, you're already running too cool, then again, who knows for sure what the REAL temp is.
It's not at all unusual to see these motors at 87-90 in the summer while underway, especially with the A/C on. At idle in summer-like conditions, 100-105 is also not unusual.
Cars were designed to run hot; there's a fine line between hot and too hot.
Stick with an OEM 87 t-stat.