The 4 ohm rating is the nominal rating which will be what the amp sees with the speaker in use. To be safe I would use the nominal rating for the hookup. I would connect one speaker on a channel and crank it up and check the amps temperature. Then connect the second speaker on each channel, crank it up and make sure the temperature isn't excessive.
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
Large Advent Loudspeakers/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590
Home Theater System
Onkyo PR-SC886/7125/Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioners