Back on topic. There was a
1992 paper by Janoo and Gasc that analyzed the predatory strike of
Vipera ammodytes using high speed cinematography. Obviously vipers are a completely different lineage than pythons, but it does provide some interesting data regarding what some snake lineages are capable of. Based on their results,
V. ammodytes was capable of performing a
complete strike in 0.33 seconds, and took only 0.0375 seconds to impact the prey item. This corresponds to 1.47 m/s or 5.29 km/h (3.29 mph). The authors also filmed missed strikes by a rhino viper (
Bitis nasicornis) and a gaboon viper (
B. gabonica), which were produced in 0.2 seconds and 0.42 seconds, respectively. The strike speed up until impact was 0.39 and 1.55 m/s, respectively, compared to 1.32 m/s in
V. ammodytes.
Janoo and Gasc (1992) also mention data by Van Riper (1953, 1955) on rattlesnakes, which produced defensive strikes at 2.47 m/s, which corresponds to 8.89 km/h (5.52 mph).
The poor sampling and lack of repetitions don't really allow for general statements based on that study, but it does provide some interesting minimum values.