A tremendous amount of very technical information by experts has been recently written about overheating and coolant, and, I am sorry to say that a large part of what has been written has gone straight over my head. The term overheating has also come in for a lot of criticism of late and my thoughts on that are more what you are comfortable with, until the amount of heat, becomes mentally uncomfortable.
Let me say that my field of expertise was not in Mechanical Engineering, nor Chemistry, but Law Enforcement, so I cannot speak authoritatively on the subject other than personal experience. People say that there is a difference between the MGB GT V8 and the RV8 with regard to let me just say cooling. That may be the case. I have owned just 1 MG, an MGB GT V8 which I have had for over 36 years. From 1976 to 2006 I used the car in standard form in the UK and in Europe. Rightly or wrongly, I liked the temperature gauge to read up to Normal, but I was strangely happier if it read just below. I understand that the RV8 was designed to show Normal on the gauge even if the temp of the engine was not, however some folks with electrical expertise are able to make the gauge read more accurately.
In the Summer, particularly in Europe, on occasions, I felt uncomfortable with the position of the needle, so put in a 74 Deg C stat which helped. I then started using MGOC's Forlife fluid which is similar to Evans coolant, the differences being that For life has to be changed after 10 years and its red colour changes to indicate head gasket failure and then after the repair it magically changes back. I am on my second batch of forlife fluid after using it for nigh on 16 years. After 10 years at the coolant change, there was no internal contamination and the fluid came out clear, like red wine. It has done what it claimed and I was pleased with it.
In 2006, I moved to Texas where we have regularly temps in the Summer of over 100 deg, and I am back with getting hot issues. This is of course somewhat extreme. So in an attempt to be mentally comfortable, I am again investigating the issue. Thus far I have fitted the Big Bore Thermostat, and an Aluminum Radiator. I am still not there yet and am waiting for the Buick 300/340 short water pump which will fit and it has parabolic impella's.
I am considering changing to the Evans coolant myself as it is more available here. As far as cost is concerned, I think that in the long term with Anti-freeze changes recommended every two years, I think this is the cheaper alternative. You do of course have to evacuate all the Anti-freeze, including the heater, and top up ONLY with this fluid, not water.
In short well worth it, cost wise too, just fill it and forget it. I hope this helps in your decision.