How come importing the bootstrap.dat to Bitcoin Core takes so long? So I downloaded and installed BitCoin Core X64 v0.9.3 from https://bitcoin.org/en/download.

I then downloaded the linked bootstrap.dat torrent and after it downloaded the bootstrap.dat, I moved it into the root of the Bitcoin program folder.

I started the program, and here I am, about 20 hours later and its still synchronizing with network... I've got about 4 weeks left to go.

I noticed in my Bitcoin program folder, my bootstrap.dat file has now been renamed to bootstrap.dat.old.

I'm just curious if this in normal for the time it's taking to sync a downloaded bootstrap file. Not to mention running my CPU at 70% the entire time.

My PC is an AMD 8-core with 16GB RAM, and internet with 50mbps down and 25mbps up speed.

Thanks for any advice.
When you bootstrap the database of your Bitcoin Core, the bootstrap.dat contains all the data necessary to build the database, but your computer will still build the database from ground up, verifying each and every transaction of each block. So, compared to the regular synchronization you just save the downloading of individual blocks. Once the bootstrap.dat is renamed to bootstrap.dat.old it has been completely imported and can be safely deleted.

Now, in your case, the bootstrap.dat was probably a few weeks old, and your computer is getting the remaining blocks through regular synchronization. It will download one block, verify all content, update the database, and repeat, until the it has caught up to the current state of the network. 

For the whole process the bottleneck is usually the CPU, as it's mostly computation, or the harddisk i/o. The necessary download speed is much less than 50mb/s, though it is quicker in total if all data is already available on the computer. It is common for this process to take hours to days.

As Jannes and David pointed out in the comments, synchronization performance will generally be improved with the upcoming 0.10 version due to the introduction of headers-first synchronization.