One important aspect of the test (separate from colour casts and UV light) is how Ektar handles bright skies. We've used Reala for years and came to expect a certain performance. I read that Ektar is difficult to expose and tends to produce an unnatural hyper-saturated look when overexposed by several stops. Well, we've produced some seriously overcooked Ektar negatives in 120 recently and the colours & contrast range are still excellent.
We're seriously considering switching to Ektar.