Investment in their network has paid off for Slingshot, making them the lead ISP due to "significant investment in bandwidth and caching" according to their Chief Technology Officer, Adrian Dick. Slingshot's improvement was across the board for both Surfing and Speed consistency. Coincidentally, TrueNet separated Slingshot's Capped vs Unlimited plans and found thatSlingshot is performing as well as the best ISPs for the most common capped plan while their Unlimited plans are better than some ISPs capped plans.
https://www.truenet.co.nz/articles/september-2012-report