It's not really the network speed, it's what you're transferring. Transferring input from your iPhone to that desktop and then you're wanting its display sent instantly back to you at a cruisin' 30 fps? Face it, VNC is a sloooow technology. It's only meant to be used for accessing a computer without a monitor, really. It's not at all meant for gaming using an iPhone, don't ever EVER expect it to do that.