Now would the ST4S compare so favourably to the SPS dyno run because it's for sale?
Only kidding, if I had any spare dosh I would be highly tempted by your 4S.
Apart from the 20 Kg extra weight of the 4S, what about the SPS flywheel? Isn't that lighter, making the SPS spin up faster and feel more lively. Also, what gearing have they both got? ST's are notoriously overgeared, might need another cog or two at the back to approximate the SPS thrust