Yes, the 5 point breastplates are most commonly seen on eventers, but there are becoming more common with show jumpers and field (fox) hunting as well now.
The 5 point is the most secure style of breastplate, that is why I suggested it, seeing as though you are having very obvious saddle slipping issues with your saddle and horse.
The 5 point style would distribute the pressure over a greater area than the other 3 point styles, seeing as though it also attaches at the lower girth billets/higher up on the girth straps, as well as at the regular attachment areas of the saddle and girth. With the regular 3 point styles, with a saddle that is prone to slipping back while ridding, the pressure can be very high on the 2 points of attachment at the top of the saddle which then causes more pressure to the horse in that area as well.
It's up to you which style you choose to best fit your needs. If you think one of the 3 point styles may be enough to do the job that you need it to do then I would definitely recommend one of those styles, but if the slipping issue is a big problem, the 5 point may be best regardless of what discipline you do and whether or not it is commonly seen in that discipline.
Would it be possible for you to try out the different styles? If you know someone who could lend you theirs to try out that could be helpful in deciding which style would work best for your needs.