Is high temperature an issue with underfloor heating?

I have in floor heating (pex tubing in lightweight concrete) and it's inherently slow. You can't do normal "setback at night" sort of programming and expect 6-8 degrees of recovery quickly in the morning like you could with a forced air furnace. My system also has an outdoor temp sensor that varies the temp of the water supplied to the floors. If you have a large thermal mass (like concrete), it's prone to overshoot the set point.

To be more specific to your question: Pushing the supply temp to 60c (140F) would not be wise even if the piping and flooring could take it. The floor would get uncomfortably hot. 50c (122F) might be ok on coldest days.

Tell us more about your system. Boiler type? Control system? Flooring type? Type of tubing?

This may not be an answer, but I had too much to say to put it in comments. I'll update this to be more consistent with an answer if you respond with more info.

One issue is the pipe material - it may become to soft and then burst due to the pressure or a rough surface could split it.

Another issue is differential heating could crack the slab if it is in concrete.