Thanks for all the input guys, very informative but I may have misled with my initial question, so to tighten this and not run the risk of repeating what's been covered before.....unless this has been covered before....to which I am obviously oblivious
I'm hoping to explore the possibility of battery control in S7, to maximise battery life it makes sense to reduce load and thus by default ball races would logically be a good place to start, not just gear boxes but all major axles with the heaviest loading, tenders and drivers, ponies and trailing trucks would fall outside that area I feel.
So going one step further would all ball race axles be of benefit? if yes then by default you will have little to zero side play, if you then have no side play, will that piece of rolling stock then become pretty useless at travelling through most point work. If it were my layout I could simply fudge the track to accept the rigid wheelbase, but if wishing to use it elsewhere it obviously ain't gonna work! Zero side play also negates the need to split main rods to allow for lateral play, though that may fall outside of the 'S7 ethos'.
If ball races make next to no difference to load then plain bearings is the simple and obvious choice and the debate is closed....bearing in mind the advice given above for plain bearing chassis with regards to side play.
If however, ball races give a marked improvement, then I feel the possibility (personal) to explore further should be taken up, even if it's all theoretical. One way I can see around this would be to fit the leading and trailing axles with ball races and zero side play and the intermediates with plain bearings that allow controlled side play.
This then leads onto springing and is it really required, ball races lock lateral play but could also lock vertical play, vertical play could be introduced on the intermediates only. One could also argue that horn blocks may not be needed, the ball races simply sitting in oval holes, it might pay to add NS to the inside of the frames to strengthen the oval holes to match the brass holes in the frame....actually thinking further left field why oval holes, simple slots would suffice. This would increase the surface area in contact with the bearing and thus reduce the wear imparted by the steel ball races. Some method to stop the outer race rotating would need to be employed.
In short, I'm wondering if we are over engineering models because of past habits or practices introduced by older technology, yes it is very nice to be fully sprung in authentic horn guides (I accept they are mandatory if you can see inside the frames, ala 9F) but is it really necessary if your PW is up to scratch. Eastsidepilot has already show that horn guides simply fitted to frame slots with out the rest of the package work just fine, are there other simplicities that can be used or explored?
Sorry just spent all day in an out of the box management thinking course, can ya tell LOL
Kindest