That was an interesting diversion in Early Risers, though it took some tracking back to follow it all. I don't frequent that thread, so was a bit miffed to see serious railway discussion taking place.
Dave, I don't think you can lay blame at Tuplin and Nock as being at fault for the continued view that the Midland had a "small engine policy". I don't think David Jenkinson and Bob Essery would have been unafraid to re-appraise earlier thinking, but they reach the same conclusion despite both evidently having fondness and respect for the MR. That said, I think they were thinking more of the effect of the Midland approach in the early days of the LMS. There is no denying that the Compounds were good sized engines both when first built and when Deeley's full production started. However, that was 1905 and 1907 and, apart from superheating them from 1909, that was it. In terms of passenger locomotives the MR then continued it's programme of rebuilding the smaller 4-4-0s into the 483 Class 2P and reconfiguring 0-6-0s up and down power classes. At the same time the fleet of 2-4-0s were still very active and over 250 came to the LMS. The Midland just seems to have stopped locomotive development (beyond the drawing board) for itself after Deeley left. The 4Fs were a 1911 design and didn't really meet the needs of a company with such substantial long-distance coal traffic.
Elsewhere similarly sized companies (and some smaller ones) were developing 2-6-0s, 4-6-0s and 0-8-0s. Admittedly, there were not always a success, but they were addressing traffic needs. Maybe it could be said that the Midland kept its traffic needs and locomotive design in balance (taking into account a desire to avoid expensive civil engineering works) and managed itself pretty well (apart from the London-bound coal traffic) but I think what irks and leads to folk like me teasing Stephen from time to time about MR motive power is the imposition of that thinking on the LMS. The Compounds did consistently fine work on turns that matched their design brief, Euston to Wolverhampton for example, but were never going to be suitable as a WCML prime mover. The 4Fs, not withstanding Adrian Tester's attempt at rehabilitation, weren't big enough or sturdy enough to be the prime freight locomotive for the system as a whole and there were just too many 2Ps built.
On speed, I think there were quite a few free-steaming big-wheeled 4-4-0s dotted around that could probably get up to 85-90 mph in favourable conditions, the LY Flyers and the Dunalastairs leap to mind from other bits of the LMS. That's not to decry the work of Midland engines in that regard; they ran freely, were very well looked after and I can't recall hearing of any Midland class having steaming problems at all, unlike a host of other designs.