Here's what I have found....
The answer to your issue depends heavily on whether or not you plan to intercool the second stage, or run it into the engine directly as I have.
If you do plan to intercool stage 2:
Then yes, I believe the stock integral wastegate is adequate to hold the charger to 20lbs. Or at least the 1.0 housing on the BB would have done it with it's integral gate. The stocker with the .84 housing might be a little dicey, but I think it will work (Good enough to save you the time, money and trouble of adding an EXT gate) Then you can run around 20lbs per stage and be all happy.
If you do not plan to intercool stage 2:
Then no. This is the biggest reason......my 44mm gate is TOO SMALL right now.....
If you don't intercool the second stage you will not want to balance the stages. You will want to run absolutely as much pressure on the first stage (intercooled) as you possibly can. And that means that the second stage will be doing as little as possible (lowest intake air temp). Right now I run about 25-27lbs on the 47 and about 7-10lbs on the 38R when at full boost. Now on the bottom the 38R might make as much as 30lbs alone, but once the 47 starts coming online it takes over and the egts actually start dropping as the power starts coming up.
I have actually removed material from the end of the valvestem on the Tial gate to allow more lift, and also cut about an inch from the lowest rate of the large diameter springs they offer in order to ensure that it is absolutely bottomed out open when I'm up on boost. I wish I could hold that charger down to 4lbs or so. Then I could run upward of 30 on the 47 without popping the manifold.
The other issue is, what manifold boost are you looking for? If I were running say 60lbs instead of 50, that same 44mm gate would all the sudden be more than enough. But at 50, it's asking a lot of it to keep that 38R settled down.
Just my experience with it.