The track specification is entirely appropriate for running 100-ton locomotives at 25 miles an hour. If we were aiming for an inappropriatly extravagant specification for higher speeds then the ballast bed would be deeper and thus more costly. If we used second hand rails, then we'd be replacing them again in another 30 years, as we are with the current rails on the track north from Horsted Keynes, which have now been there for 30 years, and the sleepers are due for replacement too. We are making use of a top spec tamper simply because it's there for crew training. The rails on the SP-HK section were anything up to a century old, on formation that was built 140 years ago. Fitting brand new rail now, on a decently overhauled formation is a question of doing the job properly, not "over spec", just so that it lasts, with appropriate maintenance, for many years into the future. And we're already seeing the advantages with fewer broken loco springs, and less tyre wear :-)