I think once you are 'sucked' into these finance deals you never escape
Your clearly putting in a lot of wedge, £23k. But, can you really find another £22-28k in 2/3 years time? I doubt it (nothing personal), therefore you will have to permenantly keep swopping around and never own one of these cars, plus your £23k capital is going to deteroriate like a mother over time as you down grade/swop
The below excludes the baloon payment, and treats the payments as a loan (not strictly correct I know!).
Your first deal means you have paid £12,240 (36*£340) for a £6k loan.
Second deal, £14,004 for a £8k loan.
Third, £6,504 for a £2k loan.
These dont sound good to me, maybe a £23k plus loan motor (£30k in total) is a better option
Personally, those kinda rates would break me
Good luck
£0.02
Dave