Never heard of cooling issues? I do think it will be as reliable if not more reliable than a boosted VQ. Certainly a lot more tunable as I've pretty much hit my maximum without uprating everything again on mine to benefit an extra 100+ bhp.. Just converting to RB I can be looking at 450 - 500bhp as standard
I reckon I would make quite a bit back off the VQ TT lump I've got at the moment to benefit what's needed for the RB26.. I've estimated around 6k for everything I need from engine/trans, mounting kit to loom and custom prop. (not including labour and any custom fabrication obviously).
Is 450-500 not like the max you can get out an RB without fully building a forged engine with a lot bigger turbo/turbos? And you're VQ could achieve more than this if it's forged. I personally think 6 grand is way off as you will have to buy all the new fuelling system to support a big power RB, then the big single/twin turbos,intercooler, engine management, mapping aswell as all the machining and porting and an engineering shop for the oil system and then there's cams, valves, springs, the list is massive but if you have the money go for it. And like you said you will make a good bit of money back from the TT VQ engine and i also might want to take it off your hands