I used to own a JD and you shouldn't have any problems getting a ball up the ramp at all.  You do have to be very accurate but flipper strength shouldn't be an issue.

If you do buy a JD, make sure you do the Deadworld mod if it hasn't been done already.  It makes a huge difference and is much better.

+1 I had a really nice JD and never had any problems making any ramps as long as the shots were pure.