Pretty much the same top speed I get on my similarly geared derailleur bike.
A Sturmey-Archer XRF8(W) IGH fitted with a 19T cog, driven by a 53T chainwheel and on a bike with 700Cx23mm tires would have a 238 gear-inch top ratio. Pedaling 90rpm on the cranks, this would give 64mph.
See starting 2:17
here.
Would you void the Sturmey-Archer warranty if you tried to accelerate your 23mm tires to cruising speed by standing up on level ground? Sheldon Brown's site has a very good gear table and all the major IGF hubs are represented. Elsewhere on his site are the minimum cog size (and maximum chainwheel size) that can be used safely with the hub. I'm thinking an effective gear of 238" falls outside of specs even if it is obtained using an approved cog size.
H