The issue the OP had with pressure is that the heatsink/peltier were insufficient to extract heat. The FPGA was injecting x watts into the working fluid and the heatsink was removing y watts. y
Yeah. Its not just about the total watts. At higher temperature delta more watts is going to get transferred. It is very possible that with same setup 50C liquid cools just fine...
I probably wasn't clear but that is what I was saying (or trying to). Too bad the easiest change (working fluid with higher boiling point) isn't a cheap switch. Still very cool experiment.