5x5 for now but what is best for MASS!?

Hey guys I run the 5x5 system right now and I'm sure most of you know what it is by now. How long do you run this and also is this good for mass or more for strength increase? I'm looking for a great MASS gaining workout to pack on some size instead of the one I'm using now. Thanks to any who respond!

Is this Bill Starr's 5x5 (the very famous one that's been around for decades) or is this the one termed 5x5 here that seems to be popular with a 3 day bodypart split that does the core exercise for 5 sets of 5, uses a higher rep scheme for a lot of assistance work, and ends up training each muscle group once per week in standard bodybuilder fashion?

There will be a huge distinction in what advice I give depending upon which you have followed in the past. However, the one thing that will be constant is that your strength and size will be nearly totally driven by fundementals like squating, benching, and pulling (whether that be deadlifts or powercleans).

I use the core exercise for 5 sets of 5 then do 2 sets of 8 for 2 other exercises. It seems to work at times and then somedays I don't get too great of a pump. I do squats, bench and deadlifts so I'm not neglecting the big movements.

The first thing is that there is zero correlation between a pump and strength/size progress. Huge gains have been main by never getting a pump. There is a signficant correlation between pumps and injuries though, specifically when one does a significant number of repititions early in their warm ups.

Second, I'll tell you right away the program you are using has a few major issues:
1) It's based purely on supercompensation or single factor theory and that tends not to work over extended periods especially if one is natural.
2) There is significant assistance work. For optimum progress, one needs to increase the core lifts. Assistance work needs to be specifically targeted to weak areas affecting the core lifts. The way most bodybuilders use assistance work is the shotgun apporach and it serves mainly to eat away at recuperative capacity that could be better unitilized.
3) The overwhelming majority of programs used by high level strength and conditioning coaches to add mass to their athletes are not arranged on a 3 day split and the frequency with which the core lifts are performed (or let's say major lifts) are much higher than once per week. To get good at something in life, one has to do it fairly often and for the body to become good and progress at a movement it takes more than once per week to trigger optimal adaptation (this is why assistance work is chosen and implemented very carefully, you want as much of your recovery free to work on the core exercises as possible).
4) What does this program do right and why do people have success. You are focusing on the big exercises in the proper rep range. Working even modestly hard, they are so effective that you will progress in spite of many sub-optimalities present.

The stickies on this board are excellent:
http://forum.mesomorphosis.com/forumdisplay.php?f=3

This is by far and away the absolute best use of your time. It is written by one of if not the best strength coach in the nation and provides a full description of the real 5x5 which is still in heavy use today - I highly recommend you use this program as it is very hard not to gain weight on it. You will want to read the whole thread - it will profoundly change the way you think about your training and with luck, you won't go back to it:
http://forum.mesomorphosis.com/showthread.php?t=12

This is my implementation of a 5x5 for bodybuilders. You will notice the volume and intesity waves as well as deloading worked into it. I would use this one if I were to suggest one to you. It is based on the Bill Starr 5x5 and the basic 8 week squat example in the link above. Similar workouts are used by the best athletes in the world for at least part of the year and are very result producing even to the point of forcing fairly severe diet restritions on athletes who are close to a weight class limit or for whom too much added mass would take away from performance (think sprinter):
http://www.fortifiediron.net/invision/index.php?showtopic=3989&st=0&p=69541&#entry69541