I think the T500RS will probably feel more natural, that is the case of the more expensive wheel sets I believe but the lower price range it is unlikely to feel close to real due to not being as smooth.
I'm the opposite in terms of controller vs wheel times. I got my DFGT in February 2010 and within an hour I was knocking seconds of my best control pad times. I agree with you about the ability to catch twitchy cars is much easier with a controller but with a wheel you have the precision to prevent it from being at a point you might lose control.
Isn't the G27 badly supported in this game as you can't change the strength of the force feedback and also the clutch functions strangely. Anyone correct me if I'm wrong as I'm going by memory of what I think I read on this forum
. I think it is unlikely that person will find the G27 amazing.
I have a DFGT and can say it is amazing for what it costs and the buttons are very convenient being an official wheel. Horn button ftw

. Only the pedals are a bit weak but I don't mind as it is less tiring for my feet.