SUCH a technical question for a landscape design installed years ago! Most important is that you honor your design concept with correct design decisions.
From your HOUZZ Portfolio I noticed you collected photos of similar slides from other landscape contractors. If you are a do-it-yourself homeowner then simply Google "Playground slide equipment" at your location to get advice and specifications from local vendors. If not, trust your preferred landscape contractor to assist you in these decisions.
Safety, Good Fun and Practicality in Design will drive this answer.
Gregory Davis & Associates