That's a better question for 'pbsd, but 4096 bit keys are infeasible to attack (outside of quantum computing) using any technique currently known to science.

I'm fond of saying that the thing that takes out RSA-2048 is likely to take out RSA altogether, so, over the medium term, look to Elliptic Curve instead of RSA. New systems should be designed with ECC instead of classical IFP/DLP crypto.