Speaking within the context of https SSL certs, is there any real value to a key/cert above 2048 bits?

The reason I asked: updating a few certs at office recently I nuked an older F5 LTM device by installing a 4096 bit key/cert pair - the load on the appliance (Linux based) shot up from less than 1 to about 30 and became so excruciatingly slow it was nearly impossible to back the change out (web GUI and ssh were both nearly non-responsive)..

On modern hardware, including modern F5s, this problem doesn't exist... but from what reading I've done it seems 4096 buys you very little anyway ?

With a theoretical quantum computer attacking is there any significant gain with the bigger key size?

Curious what others think....



John
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