I know you only considering RTC and Wykii, but might i suggest marble pim? they are very active. They interact during feeding. Got super long whiskers that stick out of water during feeding. And he will be good for your 8x4 very comfortably for life.
Of course, if i were to choose between your options i would take RTC (biased?) ... never kept a wykii ^^
PS: growth is equally phenomenal as RTC
Of course, if i were to choose between your options i would take RTC (biased?) ... never kept a wykii ^^
PS: growth is equally phenomenal as RTC