Usually on a system like 5X5's, you remain on it for 3 month. Than after a break of 1 or 2 weeks try another system, (may also be 3 months or so). Something that may be easier on your joints and CNS. When you start missing or falling short of planned rep's, that may be the first clue that you need a change for awhile. Do try 3X8-12, which can be more joint friendly for you. I usually switch to 10X10's after a longer period of PR and heavy partial rep training. Always better on the joints and can help increase strength and form in the off season. Good Luck.