Background processing: faster or slower?

[mav]

Hi  guys,

My question is very simple, but I haven't been able to find an answer. So maybe it could be useful for other people.
 
Will running a job in the background speed it up?
- speed it up (no GUI refresh), which is what I imagine,
- or slow it down (background means lower execution priority)?

Thanks in advance for your answers!

[olihar]

Identical speed.