I've used the original Mead Springs in my Sovereign for years now and I swear by them. Iirc I put a first-valve spring in my 4th valve though because otherwise it wouldn't come up fast enough for my liking... although I can't remember if I put a 4th valve spring in the 4th valve when I replaced them 2 years ago
By the way, does anyone know if the Mead springs fit in Willson valves, or are they too long? Since the stock springs in Willsons are a lot smaller I've not tried that yet but I've always felt that the valve action in mine was a bit 'loose' for my liking, but I don't want to accidentally screw up anything by trying it out willy-nilly.
Euphoniums
2008 Willson 2960TA Celebration
1979 Boosey & Hawkes Sovereign (Round Stamp)
Mouthpiece: Denis Wick SM4
Baritone
1975 Besson New Standard
Mouthpiece: Courtois 10