I always lean towards the bigger tank when faced with that kind of choice. Removing the rim on that size tank would certainly cause my pulse rate to go up during the first week with water in it, but, as I see it, with the water level 6 inches from the top, for example, the seams near the top wouldn't be unduly stressed, since the area above the water level would be somewhat equivalent to a Eurobrace in resisting the outward bowing of the glass. I know my de-rimmed 10 gallon tank seems perfectly safe when filled similarly.
If you had a 75E tank, I would be pumped up about using that instead of the 50. As some say, "bigger is better".