Just to amplify on what tirwhan said: Get the job done before making it faster. Often, you'll find that it'll be fast enough. When it isn't, you'll often find that:

1. Adding CPU/RAM/DISK/whatever may be cheaper than coding time.
2. Improving the algorithm may be enough to make the system fast enough without recoding in a new language.
3. Your processing time may be dominated by I/O time, making the language you choose irrelevent.

Back in the old days, I often hand-optimized code in assembler or C to make it fast enough. Now I rarely find the need. I frequently do some serious processing on fairly large files, and the processing time is small compared to the I/O time. So it would be faster in my case to get faster boxes of disks rather than spend any time on updating algorithms, translation, etc.

...roboticus