I am hoping the S40 will be able to climb the 15% hills I need to climb fast enough so won't tip over.I have a Catrike 700, Cruzbike V20 & Silvio. Catrike is definitely slower than the Cruzbikes. You will enjoy your S40 once you have transitioned from three wheels to two wheels. Maintaining a higher speed to keep from tipping over is the key. My Cruzbike stall speed is about 5mph before tipping over.
The slowest speed really depends on how we you can balance. Initially it will be higher as you are getting used to the Cruzbike. The more miles you put in the better you balance will be and the slower you can go without tipping over.Is it 5mph for both bikes?