MisterP:
I think you need a test drive in a GTI to decide whether you’d be prepared to pay an extra £155 a month for minor performance gains (more prominent at the lower end) and a few red stripes.
You’ve got to ask yourself what a GTI has that a GTD doesn’t, and how much you are prepared to pay out to get out of the GTD and into the GTI.
Small performance gains? 0-100mph GTi PP = 14.1 Seconds - GTD = 18.5 Seconds ....
Top Speeds? GTi PP = 155mph - GTD = 143mph
Goodbye GTD!
Potential to get the diff, sharper turn in and more stable (read better) handling, better brakes, the ability to rev to 7,000rpm, really broad powerband, no "taxi like" rattle - a properly rorty engine note, no "tramping" from a standing start, etc.
No matter what VW are trying to suggest, the GTD is not a diesel engined GTi - there are loads of differences!
I used to have an A3 TDi 170bhp Quattro in S-line form (until last week); and it wasn't a bad car, but my GTi would run rings around it, everywhere! My advice to the OP is if you want one and can afford it - buy a GTi PP and relish it ......
I don't think anyone has mentioned the PP at all in their conversation, this thread is about the cost to chop in the GTD very prematurely for a GTI, add in a PP then we're talking £6k to £7k for the OP and MisterP to trade in.
No one is under any allusions about what the GTD can do next to a GTI from 0-30mph. Take the comparisons from 40-80mph (where most people will be using the power) and the 4 second gap your example showed is more like a 1.5s gap against a standard GTI.
If the OP doesn't care too much for off the line acceleration (which hasn't been established) then maybe a tuning box for about £360 might be far more acceptable than chucking £5k at a car that will perform comparably above 30mph to a standard GTI in handling (a manual GTD is only 4Kg front heavy vs a DSG GTI - 20Kg won't ruin the handling) and in-gear performance (i'd take an educated guess that a tuning box equipped GTD pumping out 229PS and 500Nm would outdo a PP in a straight line from 40 to any figure you choose above 70mph).
£359 or £5k - it's quite a difference. Buy the car you wanted from the start and you're talking £550 GTI/£1500 PP. I would never let the RRP difference stop me picking the GTI if that's what I wanted, but when it's going to take you from £350 a month to £500 a month, it's going to take some thinking about. Keep that GTD for 2 years and you'll probably only lose an extra grand over changing now.
If I was wanting a GTI at the point of ordering then I may have gone for the PP, you do get a fair bit for your £960. A fair proportion of the outright performance is eaten up in the extra weight of the Diff and the brakes, but if you do like flinging your car around corners hard then i'm sure the diff will come in very handy.