I want to remote into a Mac Mini (4 GB RAM) from a PC and wanted to know how slow is it and is it fast enough to do iOS development?
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If you're planning to do iOS development, than the performance really shouldn't be the issue. When you're typing out code the display changes little enough that moving the display data will be trivial. Any slowness in the connection might become annoying when it comes to testing on the emulator, because the phone's screen image might come over laggy or with low color-quality depending on the technology you use. You should still be able to work fine, though, and just do your fine visual testing at the physical console.
When it comes to remote connections, performance depends on two key factors:
In general, try to use a system that forwards instructions. Unfortunately, looking up OS X remote control suggests that OS X does not provide such a system. In that case, you'll probably be stuck with VNC (if your computer can accept direct connections - e.g. routers and firewalls are configured properly if present), or LogMeIn if you cannot establish a direct connection (I do highly recommend LMI as an excellent product, but only use it when you have to).