I guess that comes down to the real speed impact. A factor of two will kill the idea of using F#. A factor of 1.2 might be okay. It all depends on the pay off.

I guess that comes down to the real speed impact. A factor of two will kill the idea of using F#. A factor of 1.2 might be okay. It all depends on the pay off. If the bug rate is as reduced as I have seen with my own tinkering then it will be worth rebuilding somethings from scratch. But I don't know how you justify the risk when there are other mainstream languages that do the job.