Hi,
The Cross Bleed remains closed - unless you select it open or you introduce APU Bleed Air.
If your engine power is set with EPR, then the Left engine works harder to produce the same EPR and supply the bleed air to the Left Pack.
If your engine power is controlled with N1 - then yes the power will be slightly up on the RH side (or down on the left if you've calculated Packs Off) - but not so much as you would notice on a normal day.