I think that 800 would be ok but just to be sure apply couple more layers of agent, or put some more effort and sand it to 2000, or use PVA because then there isn't really matter what the finish is.

~~~Everytime I hear sound of demoulding part I have eargasm~~~

I'm not that bothered about the finish of the part, it's going to be painted so does not need to be a gloss finish (if it was gloss I'd have to rub it down anyway for the paint to take to it).  I'm only worried about getting the part out of the mould.  It's not going to be a production part and only 2 or 3 'pulls'.

hi, there is a rule : better mould finish = better final part finish. When the mould is glossy it will look better and it will release better. Perfect finish is to 2000 wet&dry sand and then polish it with mechanical polisher. I think that if you want to be sure you should sand it to 1000 grid. Higher grid is better grid

~~~Everytime I hear sound of demoulding part I have eargasm~~~

What kind of surface finish is required for easy lease to work effectivly?
Does the surface have to be finished to a high gloss, or would a 400 grit finish for example still work OK?