Where should I start?

Ya it would be rough on the highway. If the shocks are junk it will be mushy, you wont believe how much 90/10 will stiffen the front end because it keep the wheels from coming up into fender, so when you go around a corner it wont dive and when you make hard stops but it will lift when you accelerate. As far as gears and mph check out this link Stan Weiss' - Automotive Performance Software / Interactive JavaScript to Calculate Speed(MPH) for given RPM, Rear Gear Ratio and Trans Gear Ratio