I have driven a 1.4 as a courtesy car twice, both the Evo and the Grande, I used to have a T-Jet sporting then went to a GPA.
1.4 needs to be kept at the limit to go anywhere quick or have fun, it should be a slight bit lighter than the T-jet so this may make it v v intially pick up a slight bit quicker out of corners if in the right gear.
There is no comparison between the two worth mentioning that the T-Jet wont win, apart from obv initial costs.
You need to adjust driving style to the turbo cars as well, turbo lag is a bit of a killer in low rev situation! You quickly learn what is best gear for given revs, especially roundabouts, had one slightly oooo situation when I had first got my T-Jet and came up to a roundabout in 2nd and then revs dropped I floored it to get into a gap and pick up was terrible as it was low revs (1300-1500rpm) and I had to wait for turbo to spool and then it went while cars baring down on me!
I also found that the 1.4 sporting ate petrol compared to old T-Jet as it needs to be thrashed a bit.
I am still managing 31mpg in my GPA average, and that mixture of all driving styles. At 20k a yr might wish to consider M-Jet but weigh up all of the costs for keeping it going
Hopefully this is useful, any questions let me know!