On my Dual-Quadcore 3.2 GHz with a high speed SATA drive, untarring only took a few seconds. But, thats slightly more hardware than the N810 has.

For comparison, the bunzip takes 36 seconds.

So, using this totally un-scientific info, you _might_ be able to save 15-20% of the time. Have to try it for real to see for sure.

Frankly, I suspect it will depend on the memory card. Since there is only the one file, it should amount to a file copy from the device to the device. It's going to have to pass into memory first, since I don't think tar would be smart enough to issue a direct disk copy. The read is going to be sequential, as well as the write. I've read a few places that SD cards don't handle that as well as random. Of course, since you are alternating the read and write, maybe that's not an issue.

For somebody with a 'cheap' Class 2, it will likely take longer than someone with a 'well designed' Class 6. (I'll leave the arguments on which vendor is which to other threads)

If memory serves though, there was an issue in one of the EasyDeb threads about people using an older/non-gnu version of tar to untar it. Removing the tar would solve that dependence.