I recommend using the stock 190 t-stat. If you have a well taken car of coolants system with all hoses in good shape, clean, full flowing radiator, freshly rebuilt fan clutch, and a good water pump, you will have nothing to worry about. If there was a problem with the stock cooling system, Toyota would have done something about it 20 years ago. The reason some people seem to think otherwise is because they probably still have some of those 20 year old cooling parts on their car
. Be glad something on a vehicle lasts 20 years, that shows how well thought out and how well built the machine was from the factory. Like a few others have said, if you still have doubts, at least get a dual core radiator, make sure the rest of you coolant system is in good shape, but I'd personally keep the stock temp t-stat.
This of course changes for those (like jdub) who are running considerable amounts of power through their machine and need a little extra something to make sure the coolant system doesn't shit itself, like the bigger radiator, hard pipes, or silicone hoses, new water pump, fanclutch/electric fans, etc.