Haven't started hex coding yet but will make a start on the basics this week.
I like this as a contrast to the Berkshire. The idea of a Berkshire was "Hey if we stuff two more wheels under the rear of a 2-8-2 it'll make a really good big freight engine". The Schools class 4-4-0 was the exact opposite: "Hey if we chop two wheels off the rear of a 4-6-0 we'll have a really good little express engine".
They had to be short to fit on the turntables on the relevant lines, but they had to be seriously fast to give good express serivce. What Maunsell did was to take a 4-6-0 and cut down the length of the boiler. The firebox stayed full sized. The boiler itself has a length of 11' 9". The firebox is a whole 9 feet. For comparison, the firebox of an A1 Berkshire is about 13 feet long and the boiler is about 26 feet. So the Berkshire, which supposedly had a really big firebox, had one that was about 50% of the boiler length. The Schools class firebox was 77% of the boiler length.
Short and fat boilers are more efficient too (the firebox gases cool off more in longer boilers) and being a 4-4-0 it had really low internal friction. The overall result was that the Schools class were known for being free steaming even on poor grades of coal, really easy on the fireman, and capable of keeping up with most 4-6-0's and 4-6-2's. The short wheelbase meant tight curves were no problem, but stability at high speed seems to have been fine.Throw in great reliability and fewer parts to maintain and you have a really good little locomotive.
Presumably the shorter boiler being cooked up by a comparatively huge firebox would need water fed into it faster, but this doesn't seem to have mattered. Overall consumption per mile wouldn't change, just the feed rate to the boiler. The only catches were that the axle loading was taken as high as possible, meaning some branch lines weren't accessible, and the starting tractive effort was a bit much for the adhesion, meaning the engineer had to handle standing starts with a bit of care. Once rolling they seem to have been fine, and were known for good performance on hills.
So yeah, these little things are cool. We gotta have them.
I'm looking forward to use the 4-4-0 "Scools Class" for minor jobs in some of my future maps. A new and improved 0-6-0 DX goods is also desireable. Everything isn't about BIG American steam engines for BIG railroading. In RRT3 there is a total lack of tank engines (seldom used in the US), but it's all up to you! I shall not try to push a volunteer doing a GREAT job 
With a top speed of 95 mph, good fuel economy, fast acceleration, great reliability and reasonable performance on grades I think it'll be useful for fairly major jobs. I'd certainly prefer it to a Mallard for a lot of things.