I would say on a turbo car you also want the probe on an exhaust runner. I know it's less accurate as far as the temp goes (compared to after the collector), but you will know the temperature sooner, so that could save you a motor right there.
Determining which runner is the problem. Generally you want either the cylinder at the end of the fuel rail, or one cylinder in. The cylinder at the end will generally be one of the hottest since it's the last to see fuel if there should be a shortage of fuel in the rail. One from the end is also good because it also runs hot due to the fact it is more insulated in the block and will usually be high. You always want to probe whatever cylinder runs hottest. It only takes one cylinder detonating to blow the motor
