hi mate, you will not find any better action on any tikka than the 595, apart from the older sako models,
if you have 1000 pounds to spare put a stock on it and get a bedding job done, if you change the 595 looking for a better modern day action your nuts...
don't just take my word for it ask any gunny worth his salt, tight tolerances, doesn't most likely need the action squared like rem 700,
If your looking for options i'll be gald to put you in touch with the fella that built mine, on a 595 action,
Snap