Red tails can get to over a meter (that's over 3 feet, sometimes 4 feet) in length, and quite bulky too. However, they don't always grow so large. Expect a minimum 60cm (24 inches) for these guys, but have a bigger tank ready, because you can expect more.
RTCxTSNs don't exactly have a set size, since they are hybrids of two fish. This means that, because of genetic variation whenever a hybrid is produced, it can attain any random large size. However, you can expect a HUGE fish, considering that both the parent species are known to attain over 3 feet in length.
As far as I have seen, most RTCxTSNs reach roughly 4 feet in length. Mine grew from 4" to 10" in a few months, still growing.