I think it would greatly depend on the weight of the shafts etc, but playing an x100 at 45" would be VERY heavy and would probably come in very high on the SW scale, thus reducing Swing Speed > Ball Speed > and ultimately distance. Even without knowing the graphite shaft used and the spin/launch factors I'd say 30 yds.
FWIW, to keep your Swing Weight resonable, I'd think you'd need to play the Steel shaft around 43 - 43.5".
I used to play steel throughout my bag until a few years ago when I found graphite to be much longer and just as consistent. Also, when I played steel in the driver, I used a lite version of DG, which helps some w/ the static weight.