Ciscos, known for the bloat, can handle 2 full tables pretty easy. The 7500's RSP4 has a R5000 CPU at 200Mhz, and can load both tables in probably less than 2 minutes, which is probably as fast as my peers can dish them out. It's old technology too. I would expect any gigahertz PC to do it in a fraction of the time.
Cisco, also known for their 20 odd years (if not more) of developing their IOS have picked up a thing or two during all those years of development. I wouldn't be so quicky to assume such things as;
They have the same architectural challanges, bottlenecks and strengths as a x86 consumer platform. That their code is equally efficient. That the overhead is the same.
Anything zebra bgpd based is, my opinion, a good example in bad programming and inefficient design.
Move along. Nothing to see here.