I prefer to do skull crushers on the bench press with a full length straight bar...easier to get the weight into position, and it does not bother my wrists.
Skull crushing 135 is not hard or abnormal.
The most i've done is 205 for about three with full straight bar...that was getting hard and puts a lot a pressure on the elbows. Gotta be careful with that kind of weight...really easy to get tendentious if it is done too often...I tend to only do heavy skull crushers ever other week to avoid this
BTW...I heard jeremy hornstra (spelling?) could do skull crushers with 315...think there is a video out there. That is crazy strong...