I have a bottom swing on my modern and top swings on everything that's more than 5 years old. From my experience, there's no reason to prefer one over the other, except for the position of bottle cage bosses an/or the rear end design of a full suspension bike.
22/36/48? That's a 26 teeth difference
Keep in mind that modern long-cage rear mechs usually have a 43 teeth capacity, so with that difference at the front you can only have a 17 teeth difference on the rear end. (11-28, 13-30 etc). You'd better be building a roadgoing MTB that has the granny on there for emergencies, because that front gearing basically limits you to a road cassette.
Sure, you can put a modern MTB cassette on there, but in that case you'll have to think about almost every shift to avoid accidentally getting it wrong and wrecking the mech, chain and lord knows what else.
Don't worry, the granny is only there for emergencies!
I take your point - nonsense IMO
but I do observe correct shifting methods (ie only biggest rears on the granny and smallest rears on the outer) and my outer is 'only' 4-6 teeth bigger than stock, also using the chainring set-up in conjunction with a modern-ish M580 LX rear mech that has a slightly longer cage than my old M750
RM capacities are somewhat conservative for obvious reasons, ie you'd be surprised what a mech can do so long as you don't run big to big (why would you!?), such as a short cage M750 XT will run 38 capacity IME
Anyway, the bike runs really well believe it or not - 48/36/22 and 11-34! reason I'm pondering is that I may go back to flats from drops so considering which FM to choose. FWIW, the bike is a rigid 29er, about as versatile as you can get hence the super wide gears.
PARTS FOR SALE:
vintage Brooks Professional saddle | Specialized FACT CX fork | Columbus fork | Reynolds 531 fork | vintage Weco hubs (fixed/freewheel) | vintage Raleigh ladies frames + lots more!