The RTC X TSN was a lab created hybrid to try and provide a fast growing food fish for (I believe) South America. The belief is that they may well max out at more than either parent (as a nubmer of hybrids do). AS can be expected, this hybrid of two of the hobby's favorite giant catfish has found its way into LFS recently (though, just as with the RTC and TSN I don't know why they stock it, there can't be that many people with absolutely massive tanks, can there?)
The same level of care and size needs to be awarded to them as with RTC and TSN. (Huge tank/pond; massive filtration; very few tank mates that won't "disappear" by morning).
The max size of both parent fish is not exactly known. In aquaria the RTC often ends up around the 3.5 to 4 feet mark and the TSN can often breach 4 feet. However in the wild both are often seen over 5 feet and there have been reports of sightings of both approaching the 8 foot mark.
Needless to say I'm looking into buying one, but not until I can house one (probably around 3 years time). I believe a safe guidance given, to ensure the fish is happy, is around 3,000 gallons for one and around 1,000 to 1,500 gallons for each extra one (with corresponding increases in filtration). You probably can house them in smaller size tanks but you have to ask if it's really fair on the fish...