Hey Kosh- www.trailtech.net they make a sweet billet dash and computer setup... I have one, very top notch stuff. If you want a TACH, you may want to hold off on buying the TrailTech stuff, as I hear they are working on a new computer unit that incorporates a TACH. As for judging speed by RPMs, that'd be pretty tough as you'd have to calculate for transmission gearing, sprocket size, etc. More math than I wanna attempt. 'bout a $120 US for the TrailTech computer w/speedo. Hope that helps.
-Ren