Lin545: This is for Kerbin, this also assumes parachutes are fired out when you instruct them to do so.

Regular parachutes have two opening stages. Preopen and full open. The preopen should not happen behind certain speed or "atmosphere and heat" will destroy it. You can register these maximum speeds doing simple climb and fall tests.

When re-entrying, your total speed depends upon "total vehicle mass" (fuel weights!) divided by "vehicle friction" (based upon any surfaces the vehicle possesses) times "total orbit size" (orbit=speed x body gravity factor, bodies with stronger gravity require more energy/speed to achieve speed of same diameter).

Empty vehicle with large wings will have much better atmosphere breaking than big rocket full of fuel.
Empty vehicle with large wing area landing from 80km/80km, doing "cobra dive" is very easy to re-enter (provided, the weight distribution within vehicle is correct!! or it will flip), than large rockets full of fuel, that enter from Kerbol directly into Kerbin at perpendicular angle.

You should plan your descending trajectory to Kerbin. your descending speed/orbit based upon vehicle, move fuel around to balance (heaviest part tips down), your descending angle and technique (burning the engines at nose pointing retrograde/antiradial, or "cobra" nose pointing prograde/antiradial,or perpendicular rotation or parallel rotation). Rotation helps immensely to slow the vehicle down by increasing drag and to cool all parts equally. However it also leads to shortening of trajectory!

More dense atmosphere means more heat is produced with same re-entry speed. You get more dense atmosphere the closer you are to the ground, which means the more perpendicular trajectory to Kerbin are more suicidal.

Neverless, staying too long in the upper atmosphere layers at high speeds will cause overheating due to atmosphere plasma and lack of sufficient amount of atmosphere for any cooling.

So, given the breaking technique strongly depends upon vehicle mass and drag, the most safe landing is achieved via gliding, perpendicular descending trajectory.

Under observation of everything above, you should reach speeds below 250m/s already as high as 5Km. For very heavy vehicles without much surface area, one can use drogue chutes and A.I.R.B.R.A.K.E.S to help. Drogue are much more efficient, but have netherless the risk of burning down. AIRBRAKES dont.