I just checked Yojimbo's stats from a FAQ, which makes him as fast as Ifrit... with slightly more HP than Ifrit, less Def, and 122 EVA.
... wait, what.
Ifrit:
HP MP STR DEF MAG MDF AGL LK EV ACC
3067 68 46 84 62 62 30 17 22 20
Yojimbo:
3064 0 61 73 48 69 30 17 122 38
Anyway, his Zanmato attack is dependant on a number of factors (motivation, zanmato compatibility, summoner compatibility) that can fluctuate, so I'm definitely not inclined to give him a turn1 Zanmato for "I win!" off first turn.
ESPECIALLY considering that in best case scenario (Motivation at best, Zanmato Compat of 1-3, Full Overdrive, Summoner Compat at 240+) his odds of using Zanmato is 58%. That drops to 55% without Overdrive, and at starting Summoner Compat that is around ~150, so 38% chance to use it sans Overdrive. Also, you need to pay a sum of Gil equal to or greater than 536,870,912 Gil. For 4,194,304 Gil, with maximum Compats, you get 38% chance at best of him using Zanmato.
All things considered I'd say 30% is a normal number to take, since maxing summoner compat isn't fast (you start with around 150 iirc, and you get +4 at best from him using Zanmato, and get -1 for him using Daigoro, -20 if he dies/is paid 0 Gil, -10 if he is dismissed immediately after summoning, etc.) and that is not turn1. It's not even turn2 to me.
source of this information:
here. It's a big read, though.