That makes sense as to why PGP keys are being cracked so much faster. If 88 bits is 25 times harder, then 512 bits is about 145 times harder, and that would take log2 145 = 7.2 doublings of computational power. Realistically the doubling rate is more like 18 months, so 7.2 * 1.5 = about 10 years, which is what we're observing.