My gut reaction would be it's 2 ends of the simbin "physics" extreme.
The radical has near arcade physics and is laughably easy to floor, and the caterham is one of the most extreme examples of simbin's flawed uber-understeer model.
By the by, I drove the 10 year old to MK the other day to buy a new game and it'd been the first time I'd driven after driving hundred of hours in the sim...and it was profound just how wrong sims are.
Even the just the basic visual presentation. I was showing him, telling him to look out the window and did he see the steering wheel without looking down? No. Was half his vision taken up by the wheel and dashboard? No. Any of his vision taken up by it? No. Could he see the roof? No. If I put a helmet on his head, did the helmet start 3 feet away on the windscreen like it does on the monitor? No. Would you sit 3 inches away from your TV so the helmet / wheel drawn would be closer to the right place? Not likely. Would the fact that it would be 40" wide on the TV make you wonder how big Simbin must think the human head is? Has he ever seen a racing car driver in a WTCC car that wasn't wearing a helmet? No...So why don't they draw the helmet then?
And he's 10. Imagine how much chance the 6 footer sat next to him has of seeing the steering wheel under his chin, being held in his hands, if a 10 year old sits high enough to see out the window
Then, on crappy road treaded tyres, FWD, tuned by vauxhall to understeer, in the wet, I showed that I had more grip than a fantasy sim race car does at road speeds. I stomped on the pedal round a few bends, and as you'd expect the car just followed the line. I didn't have to saw away at the wheel to, well I dunno, why do sim racers saw away at the wheel like that? Brake with my left foot or slow down or whatever sim fantasy land has decided a mini with slicks that's race prepared on a dry track needs to do because, obviously it has a lot less grip than a road car in the wet
Anyway, the radical should trounce it if I'm right and the bumper car / lawn mower TV show you guys are showing is typical. But either way I don't think they're matched....the Caterham is supposedly famous for being too fast to race.