If you can get the Tuner to adjust the two OEM radiator fans to turn on sooner and at a higher percentage then you shouldn't need to upgrade the radiator.
The Whipple Tune I'm running has the fans turn on at 175 and if it ever gets to 210 they go to 100%
That only happens when I sit in stop and go traffic and it's a heat wave.
Having said that if your going to be off-roading hard and/or towing a lot then I'd go with upgrading.
There is a member that hard wired the two OEM fans to turn on 100% all the time, he's happy with that.
Not sure if that's a good idea for people that live in cold climate though.
The cooler you run the engine the more power you'll get but mpg's will go down.
I was running the 160 thermostat for a couple of winters but realized it's just too cold so I leave the 170 degree in all year round.
Not sure if the Mishimoto is the best choice, CBR, I believe is what most guys use on the Gen 1 with good results.
@Dane put up a good thread!!!
Repositioning and upgrading the Trans cooler with fans is a good mod for keeping things cool under the hood.
Also cutting the hood vents to allow more air to escape the engine bay is a good mod.