It depends on the level of carbonation you want in the beer. If you try to push with 11 psi of 75/25 mix, you've only got 2.75 psi of CO2 on the beer. At 38F, that's about 1.7 volumes of CO2 in your beer. If you are happy with that level of carbonation, no problem. But what you have now, 11 psi at 38F, is about 2.5 volumes.
"the same volume rate" is not what I'm talking about. If you pressurize 4 times higher, you need to make your line about 4 times longer too, or replace it with a narrower line, otherwise it will just shoot foam. The system has to be balanced so that the pressure at the tap is abut 0 psi. Most nitro beers are served between 30-40 psi.
So decide what temperature you want your beer and how much CO2 you want in it. That will determine what psi you should set the regulator for. This in turn determines how long your line must be (for a given diameter) in order to balance the system. That will get you the pour you want.
Read through the draft beer quality manual, it has a lot of great information.http://www.draughtquality.org/w/page/18182201/FrontPage