speakers? i'm ashamed to say....
athena ls500's and energy c-c100 center
I would start-out at 80Hz, but would not be afraid to try 60Hz. The only issue you may have with 60Hz is when employing the center channel on things like a concert dvd. If you get a slap, just back-off on the volume a little.
I use a 60Hz x-over point, and my center channel has similar specs as yours. 60Hz helps a lot with not being able to localize the sub. It also makes the sub blend better with the mains. A LOT BETTER.
The specs for my center.
Impedance: 4 Ohms
Frequency Response: 50Hz - 32kHz
Sensitivity: 90dB
Power Range: 70 - 130 Watts
Crossover Frequency: 3kHz
The specs for yours.
Recommended Amplifier Power: up to 125 watts
Nominal Impedence: 8 ohms; Minimum Impedance: 4 ohms
Frequency Response: 50Hz-20kHz +/- 3 dB
Useable Bass Response (-10db Anechoic): 45 Hz
Sensitivity: anechoic 88 dB; 2 speakers in a typical room: 91 dB
Crossover Point: 2.2 kHz