I have used metal cored suberged arc wire before.  As long as your wire feeding is not out of the oridinary, you shouldn't notice much of a difference between that and solid wire.  The main reason we used metal cored wire is we were welding Cr-Mo-V steel and you can't get it in solid wire.  If you are welding carbon steel, your PQR results should be a slam dunk if the welding is done correclty, unless you are doing CVN testing, and then you would need to carefully review the property requirements whether you are using solid or metal cored wire.  The main difference between the two is that the metal cored wire (at the same amperage) will have a higher current density, so it should give you a better deposition rate.  However, you will typically have to balance that against the higher cost of the metal cored consumable vs solid wire.