i fly a 36" wingwarrior ezipper mkII. so far i got a mega 16/15/4 with a 6x4 prop with a castle creations 25 amp esc. running on 10cell 2/3a nimh 1050s.. i get kinda poor runtimes when i fly hot, im looking to hit around 10 minutes of flight time when i got it wot, more we be better. what i want to do is run 2 3S1P <either 4000mah pr 2100> packs in parrelel. can i do this safely? will the li poly's stay happy? my planes small but weight is not a huge issue cause i do fly with 10 cells and close to 1.5 ounces of lead in the nose.. so anyone got any pros cons to what i wanna due, also would i notice more speed from a 6x3 prop? my speed seems to be lacking for what i got, its basically got the speed of a 400 on a good day with ability to loop at level area repeatidly.... any replys answering my questions are greatly apreciated.. thanks

Actually with the 6x3 you will have more torque than speed. The 6 is the prop length and the 3 is the pitch. If you want to go faster, increase your pitch and lower your length a bit. This should improve your flight time. Try a 5x5 prop or 4.75x4.75. I run 4.75x5 and its fast enough and has 3.5 mins of flight time. Although if i were running lipo i would go 5.25x5.25. I think 6x3 for a zipper is not a good match.

so can i run lipoly packs in series and in parrelell?

Yes you can, but make sure that they are verry close in voltage(within 0.1 volts) before you try anything.
My dad runs a 16/15/4 with a 6x4 prop on 3s TP 2100's and gets about 10minutes flight time average. Of course, he isn't flying full throttle all the time.