Be careful you're not chasing something that isn't there.
I had a 1900 a series at the same time as a GTE. Whenever we took them out at the same time, to cars shows etc, the A series would always outpace the GTE until at least 60mph.
I always thought it was because the A series was lighter, but when I converted my first mk1 cavalier to GTE spec I left the four speed gearbox in to start. With a standard GTE engine and four speed box it also outpaced the GTE until at least 60mph.
The realisation when I did fit thr five speed that acceleration through the gears just wasnt as quick as the four speed was.
So if you can try and drive a couple of other standard GTEs to see what they are like.