Hi
Streamlining wasn't all to do with getting trains to run faster but was also to do with the reduction in horsepower required to run timetabled services. There was a huge public relations benefit to the companies as well with the publicity that it generated.
Tests were carried out on the LNER Gresley A4s and the wedge shaped front end was found to save 97 hp over an A3 in overcome head-on air resistance at 80 mph. The faster they went and the bigger the saving, with the difference at 100 mph being 190 hp. This meant a saving on coal consumption and contributed to the feasability of regular non-stop running between Edinburgh and London. It had the additional benefit of improving the drivers visibility by lifting smoke and steam well clear of the locomotive at speed.
The downside to it was the difficulties caused when servicing the locos with panels having to be opened or removed to carry out everyday tasks.
Regards
Brian