I used DOT-5 in a full-system rebuild in my '41 De Soto about 7 years ago.
The only real issue I had was that when I went to bleed the system, I used my 1940's pressure-bleeder tank (thoroughly cleaned-up and dried to remove DOT-3 residue).
The DOT-5 container (Cartel brand) didn't give any warnings about Silicone's tendency towards "air-entrapment"...when I put the air on the bleeder tank, I created a DOT-5 "Frapp`e", and then couldn't understand why I still had spongy pedal after bleeding the system five times!
After giving-up and letting the car sit for a few days, I called Cartel's tech support and asked them what was up with this, and after going over my situation for about 15 minutes, the tech zeroed-in on the pressure bleeder and figured-out what happened. He suggested slowly and carefully pedal-bleeding, using the time-honored two-man method, and when refilling the Master Cylinder, to pour slowly so as not to "glug" or splash the fluid and create air bubbles. If I did see bubbles in the reservoir, I was to wait until they percolated-out before going further.
The second approach worked, and the brakes have been fine for the last seven years / 17,000+ miles.
I have gone back to DOT-3 or 4 in subsequent rebuilds.
So, if you go DOT-5, my suggestion would be to avoid the pressure bleeder, and be carefull not to "aerate" the fluid.
I have also heard other guys talk about DOT-5 allowing localized pockets of water to collect in the system (as opposed to DOT-3 becoming water-logged through-out). These pockets can cause localized corrosion, become vaporized during heavy braking, or turn to ice in freezing weather...
