I have made my cake. It is about 4 3/4 inches tall. I only have 4" SPS pillars. Does the pillar have to go ALL the way down to the cake base or if I insert they as far down as i can, will it be stable?????? I have to drive over an hour with this cake and I don't want it to collapse......ANY help or advice would be appreciated.
Is the cake covered in buttercream or fondant ? I'm not sure about 3/4 of an inch but I've put sps in when my tiers were a little over but I was able to push them pretty much to the bottom. Is it a design you can transport and stack on site? It would be fine if you stacked on site. Also be sure and take the collars off the plates. This gives you a bit more height.
Honestly I think you should trim the cake to 4". I can never get my cakes exactly 4" so you are lucky in that regard.
You are almost an inch over, which I think is too much for that system. Even if you just push it in exactly four inches, the weight of the other cakes on top will definitely push the legs to the board. That's the way the system works. If that happens, you may end up with a sunken in look to your cake, or even worse, bulging or tearing, not to mention the icing looking all funky. I would definitely trim if you can, to be on the safe side.