Probably a question or an answer that is on here somewhere and I have missed it, but what was the line running speed?
Always get the impression that the trains dawdled along rather than made any great progress.
I should think that the unfitted nature of the vast majority of the freights on the line, plus its switchback gradient pattern would preclude even moderately fast running. As for the fitted freights from Woodford that had originated from York, Woodford crews would have been in no hurry as a round trip to Honeybourne could be stretched to a shift or even to achieving some overtime, as on the return trip the firemen would invariably be faced with poor steaming locos with clinker filled grates left by the WR crews. The so called LMS era express workings to Stratford from Blisworth were usually in the hands of MR 1F tanks so they would not likely to have run fast either. However the 8F hauled ironstone empties workings to Byfield used to accelerate rapidly through Blakesley station to get a good run at Plumpton Bank, so presumably other banks were sometimes charged in a similar manner.
According to the BR Sectional Appendix to the Working Timetables (Midland Div) for October 1960, the answer seems to be 45mph.
This covers the lines from Ravenstone Wood to Towcester, Blisworth to Towcester, and on to Fenny Compton - at this point it becomes Western Region and I don't have that Appendix.
There are several restrictions for junctions, such as 15mph through Towcester and Woodford West, and 20mph through Ravenstone Wood.
Also a severe restriction approaching Blisworth from Towcester where only 15mph is permitted past the distant, and 5 mph past the home signals - this is to avoid running through the bufferstops in Blisworth station!!
It would be interesting to know whether higher speeds were allowed west of Fenny C, as the track was much improved on that stretch after 1960, but that may have been to allow heavier locos and trains rather than for speed. Also I wonder whether the Stratford to Broom line was restricted more owing to the track?
I also have another document (unfortunately out 'on loan' at the moment) which details the classes of locos that were allowed over the SMJ in (I think) 1958. There are a few surprises in there to say the least ( ever thought of a 'Clan' 4-6-2 over the SMJ - apparently it would have been allowed) - but one thing that I can recall from it is that WD 2-8-0's were in theory barred from the SMJ, unless they only operated at 25mph! Probably not difficult with some of those heavy steel and ore trains, but I wonder about the empties coming the other way.
For some reason I had in my mind they only went at 25mph.
I do know, from conversation with a chap at Stratford, that freights would reverse a bit over the Avon before restarting towards Broom in order to get a bit of a head start, or so he said.
Interestingly the 1916 Appendix mentions the 20mph restriction at Ravenstone Wood junction as applying to trains travelling from Towcester with no mention of trains travelling from Olney onto the SMJ.