Well it depends on what you mean by upgraded. Replacing a cartridge style muffler that is OEM for a 200 series with a strait through design will allow a smoother path for the gasses, you just haven't gotten to the point where an increase in tube diameter is going to help, in fact it will hinder. That's the big problem, aftermarket everything is... bigger is better, well no, the right size is the right size. So I'm not saying a glass pack isn't going to make more power, it will, but the motor isn't upgrade to some wonderful level of power and efficiency with a simple bolt out bolt in. If it was, the manufactures would just use that from the beginning in this age of high MPGs and increased power while maintaining emissions.
So you take a 5.7, slap a blower on top of it, tune the engine use the increased pressure properly. Okay, but your throttle body is the same, intake manifold the same, same stroke, same bore, same fuel delivery of pump, same timing and not advanced, same internal temps from the thermostat, same heads, same catalytic converts, all controlled through a computer that is doing everything it can to never open the engine up past 70% of what it can do for longevity reasons and emissions. So how much more gasses are you putting out.
So can I get 1000hp out of a 5.7? hell yea. But a little part hear and a little part there is sadly not going to do much other than make you feel better and take money.
So to answer the question, you'll make a hp number or two at above 5,000 rpm. Anything below 3,500 or about, nope.