So this happened while trying for Nephenee... AKA builds for +spd Oscar?

You know what they say, "When life gives you lemons"...

*insert picture below*

So I still have no Nephenee, but now have SIX Oscars. Instead of whining about my "poor" luck (relative the the amount of money spent, that is), I've noticed that he has a pretty decent stat line for a cavalry unit. One of them is +spd/-hp. What would be the best build for him, and should I fully merge him +5? My next closest merge is B!Roy (+4) then Lilina (+3 soon), Ike/Ninian/Julia (+2), but most of my 5*s are unmerged. I don't want to tilt the arena such that when I use Oscar the units are too strong for the rest of my team. Yet his base skills are kinda mediocre, the only reason I might fodder one off would be to give Rally Spd/Def to Fae in addition to Hone Atk so she can partner up with my Tharja in AA/CCs.

But anyway, back to the question, what builds do you recommend? I was thinking of feeding him Ridersbane+ and Fury 3 to reach 40 spd and a decent enough defense of 29. Don't really know the rest. Maybe Desperation 3? Just don't want to waste SP without knowing how he works best.