TOTALLY up to you
What are your goals for using PT? If the sites are sufficiently similar in play and game-style, then I use the same DB...if they're different (like Tribeca vs PR) then I keep separate ones. Make a separate one for your foray into Party $50. But here's my real suggestion: create 2 new DBs for your move: one that is BOTH your old $25 and new $50 stats...and a separate one just for $50. To do this, create a new one for both by making one with a name reflecting it and choose to build it off of an existing DB (your $25 one). Then, you'll want to import all of your $50 hands into this one. Create a 2nd one just for $50 and ALSO import all of your $50 hands into this one. So, you'll have 3 DBs: your old exclusively $25 DB, new exclusively $50DB, and a new combined DB