My preference is N120 for sabots. I love the stuff but some people feel its more likely to have larger temps swings than 4198.
IMO 4198 is "safer" when shooting sabotless unless you are content with a little less speed. Take it easy if using N120 and a 300gr bullet. IIRC 55gr and a 300gr is already over 40kpsi so there isnt alot of head room....It is wonderfully clean though.
Re7 is dirty but IMO its easier on sabots and its double based so it needs less pressure to burn correctly. If you drill sabots try using a veggie wad under the sabot and Re7 if you have any.
I prefer .462x.060 veggie wads but some rifles may show a strong preference for wool wads.