Really what the temp is telling you is only half of the information. All tubing and pipe have a pressure rating at a temperature. One without the other isn't telling the buyer anything. Even the lowest strength copper has an allowable of 6Ksi. That isn' the MAWP (working pressure) of the tubing but the info you need to calculate the required wall thickness to contain the pressure. Basically, at the pressures we are talking about in a cooling system the tubing could be almost see-through and still have enough wall thickness to hold the pressure and temperature. ZERO worries from that standpoint. The connections are going to be the problem if there is one. Look at trans pan pick-ups. They get WAY hotter than 150 and they are fully submerged. There just isn't any pressure to deal with. But, as general info as the temp goes above the "rated" temperature, the MAWP of the tubing drops.