I don't have the experience that Rob does, but I have to say that I agree completely. I've been running a 7 psi cap for about 5 years now...less stress on the cooling system, and I've noticed no ill effects in terms of engine cooling and whatnot.That works out great on paper, but not on old truck engines. I learned decades ago not to trust old truck engines to anything higher than a 13 lb cap and preferably a 7. Even on olddcars I run teh lightest thing I can get away with . Older engines just have this nasty habit of springing leaks where they arent supposed to.
My biggest issue with the Evans coolant is that, if you get a major cooling system leak for any reason, you're up a creek...it's not something carried at auto parts stores, and IIRC mixing water with Evans coolant is a serious no-no.