Adobe Systems has performed tests comparing LaserWriter IINTX and LaserJet Plus. Their finding is that a LaserWriter IINTX in LaserJet Plus emulation mode is generally faster than a LaserJet Plus.
Although you can't download bitmapped LaserJet Plus Fonts to the LaserWriter IINTX, you CAN use any of the PostScript Fonts, including downloaded fonts. Unlike the LaserJet fonts, PostScript Fonts can be scaled, resulting in much more precise output.