That depended on the wordprocessor. For example, GeoWorks was amazingly fast on an XT style system; only the fastest DOS word processors were faster. If one looks at the early comparisons of Ami, Ami's speed was equivalent to middle of the pack DOS word processors. Those comparisons were for full WYSIWYG by Ami versus character mode for the DOS word processors; Ami's draft mode was significantly faster.
Note: I did manage to do most of my magazine writing using Word for Windows 1 on a 286. Of course, since the magazine I wrote for mainly covered Windows and my writing concerned WinWord macro programming, I didn't have much choice.