that mostly depends on the exact combo of parts and your use of headers ETC. but on a basically stock engine , the gains going to be mostly from about 3500rpm on up where the better flow rates and lower restriction helps the most, keep in mind that the stock intakes designed mostly for CHEAP/EASY production and hood clearance, and not a great deal of effort was made in the effort to help peak hp.
the raised port angle and slightly less restrictive ports help the mid rpm range, if you upgrade to the air strike version the large ports. even higher entrance angle and cooler runner temps have even more advantages,
but you might want to remember that the intake is part of a total system, and without better head and a larger cam and headers the full potential of that intake cant be reached.
yet either of those intakes is going to be better than the stock intake and in most cases youll notice the engine pulls to higher rpms and has better responsiveness
BTW IF your REALLY interested in increasing power you need decent heads a cam change and more compression, yeah! that all takes time,effort a a good chunk of cash, but you can make a HUGE improvement in the power levels