23+ feet was used for most of the studies RR electrification back in the 90's. The freight RR's wanted plenty of extra clearance for the double stacks. The carriers were not exactly in love with electrification, and by choosing a higher clearance, you create a lot more costly clearance problems, which raise costs and lowers the cost benefit of electrification.

I once sat through a meeting where someone from engineering pointed out that we would have to rebuild a dozen overpasses, due to clearance "issues'...... A few minutes later I pointed out that these overpasses were actually on a segment of fairly decent RR grade where it would probably be much more cost effective to lower the tracks a foot, without the need to rebuild a single bridge.

We are a long list of about 20 billion or so in much higher priority RR investments, that will be needed, long before we will be ready to spend even the kind of money we'd need to spend on electrification of even these limited segments.