The ABS diff's snout is approx 3/4" inch longer than the non-ABS, so the difference in driveshaft length would be equivalent to account for this (e.g. the ABS driveshaft will be approx 3/4" shorter than it's non-ABS counterpart. they are different length between the S13 and S14, auto and manual transmission as well.)
Here is a fairly comprehensive list of gearing for most Nissan sports cars;
http://tech.240sxone.com/500/gear-ratio ... rain-info/
and a handy calculator for the RPM/speed/gear ratio. (You'll have to input your wheel/tire info there.)
The short answer is it will result in a lower RPM for the same speed/gear that you're currently in. Most configurations have the stock diff at 4.363 for the 180sxs. I think a 3.9X ratio would be a pretty big improvement in terms of drive ability, especially if you've got or are planning to install power adders. If you're completely stock it may feel a bit more sluggish. Lots of info needed to really answer your question but use the tools provided to decide for yourself based on what your goals for the car are.
what-differential-ratio-are-you-guys-ru ... 54478.html