@tim - good advice, though are latex tubes worth it with contis?
25mm 4000Ss at 100psi on steel spoked wheels, should mean you can float along happily.
I'd go for the latex tube if running comfortably lower PSI poses any threat of pinch flatting given an individual rider's weight. If lower pressures readily accommodate the rider without threat of pinching, then butyl is a good choice.
In many cases, there won't be a great deal of difference in casing volume between 23 and 25mm clinchers if the rim is of the (still ubiquitous) narrow internal width variety. For tire volume's sake, rim width is a bigger deal with clinchers than tubulars. Running 23 or 25mm on a Kinlin XR270 might not a yield a great difference in volume; using an XR279 or A23 would accentuate the advantage of the 25.
At my weight, (57kg-ish), I can run run well under 100 psi (rear) on butyl, on XR270s without pinching a tube, but a heavier rider might want to run a similar pressure, so that would be a good application for latex- just as insurance. Otherwise, the convenience and cost of butyl makes a great deal of sense.