Decimal vs Double Speed

Question

I write financial applications where I constantly battle the decision to use a double vs using a decimal.

All of my math works on numbers with no more than 5 decimal

Answer 1

1. Floating point arithmetic will almost always be significantly faster because it is supported directly by the hardware. So far almost no widely used hardware supports decimal arithmetic (although this is changing, see comments).
2. Financial applications should always use decimal numbers, the number of horror stories stemming from using floating point in financial applications is endless, you should be able to find many such examples with a Google search.
3. While decimal arithmetic may be significantly slower than floating point arithmetic, unless you are spending a significant amount of time processing decimal data the impact on your program is likely to be negligible. As always, do the appropriate profiling before you start worrying about the difference.