Oh. I thought you were brand new with stock.
IMO, the RE500 is a joke. Anybody who owns a P2V should retire their RE500 immediately and replace it with an RE700. That's the first thing they should do. Range will increase 50% instantly.
If you already have the ITELITE, then I think your next move is to find out what your range is with the RE700. You might be perfectly happy with it. You might get a mile out of it depending on where you fly it.
If you want to put on a birdside antenna to match the ITELITE, the consensus is you need the FPVLR dipoles. This is all discussed in the ITELITE thread mentioned above.
Hope this helps.