If you plan to use automatic trading, then the only possibility is with IG (or an IG sponsored account by PRT).
Automated strategies made with ProOrder for ProRealTime only read and execute code one time per bar, at its Close, while many other platforms are trading on the ticks received by their brokers. So I think the differences you spotted come from this behavior, you are not comparing the same exact strategies.
Furthermore, different brokers also mean different data with different time settings, etc..