generally most uprated clutches have a increase in pedal pressure so they feel heavy but what you described sound like a unsprung paddle type clutch to me, they have a very heavy pedal but the thing which has made em say this is because i have had a similar problem with my old R and a few STI Impreza's
when the clutch is on the way out the pedal tends to drop and does not travel much and id also describe it as standing ona tennis ball, when the pedal first dropped on my sti, i had little knowledge of the cars and went to the local subaru garage and a few other garages.
they all told me it could either be the following, brake master cylinder/slave and a new clutch pedal.
I did not know what to do so luckily my mate's brother(group N rally driver) in law checked the car and confirmed that it was on the way out, we wnet on the motorway and the clutch was starting to slip.
thank god i did not buy all the parts like an idiot
just test out the car and see if the clutch slip's if it does not then buy the car.
sorry im not an expert or anything but just my opinion and experience and im sure it will be of help, i would not have replied until i read the tennis ball part.
good luck