I've tried different "permutations", with rounds on both, flats on the single coil, flats on the split SPB1... at the moment the single coil has rounds and the split has the flats. It sort of sounds non chronological (which doesn't make any sense, anyway, really) but I do like the feel and sound of the flats with the split. TBH, I think I like all combinations and it might be more due to the fact that now the flats are there and the ergonomics of the 57 shape vs. the slab body of the 51. What is your say? Do you have a favourite P for flats? Do you think one of the two designs is more suited to "rule" with flats?