Owned a 140 and 7ish gt4s.
Insurance wise, its about £200 dearer for the gt4 for me which is well worth it. I did love driving my 140 it was so calm and smooth compared to the gt4 but once i was back in it i loved it. 300bhp 4wd no contest.
I would base my choice on mileage now, I used to do 30k a year in the gt4 now i do about 3k so i can keep it, if i was still doing 30k i would be in a gen 7 as they are better on petrol.
Also ive had alot of Gen 7 owners lately wanting to race, i dont know why I can only assume they think because they have the newer version its faster. Needless to say it never gets old.