when i had my 172 cup..i couldnt possibly afford a 255...they were still uber money (just over a year ago) add to this..insurance..(at the time i was just about to turn 21) and it was a definate no no..
so..i plumped for a mint condish, low miler mk1..the car is absolutely fantastic, dont let anyone tell you they handle badly..the grip in the dry is unstickable unless your a complete plonker! in the wet, care is absolutely needed all the time..although, this is the same in the 255
the main differences i have noticed from past 255 drives are :
The gearbox is far far sweeter, more precise, closer, shorter ratios
The interior is in a different leauge
The mk1 clutch is more sturdy and will take more abuse
the car corners with far more stiffness and waaay less body roll especially from the rear!!
other than that...there is not much you will ever regret about the mk1...i miss mine loads..i always will..they are the original "badboy" v6...
If theres any way you can get a 255..do it!! if not..just get a low miler mk1..(watch out for cambelt changes) and you'll absolutely love it!