Hi guys, first post, so bear with me!

Currently own an RX-8 - brilliant drive, but the economy is killing me now I'm doing more mileage. So I've been looking at 140 and 170 GT TDIs. The 170s are very hard to find with leather and quite expensive, so I'm looking at 140s and would get a Bluefin upgrade on them to make it very similar to 170.
Now, I'm a bit new to all this, but are there any downsides to doing this, e.g. weakened engine components?
Also, I'm used to a 0-60 of just over 6 seconds. I realise I'm going to take a hit on the power. But the 140 is listed as 9.3, whereas the 170 is 8.3, I think. Will the upgraded 140 definitely achieve a time of around 8 seconds?
Also, is installing the Bluefin something I (as a bit of an idiot when it comes to cars - I get my cousin and brother to help!) can easily do? It seems like it from their site.
Other than that, what else can I expect from going to to a GT TDI (probably 06 plate) from my RX-8? I used to drive a 1.4 Fiesta diesel, so at least it won't be as bad as that!
Anything I should be aware of before I buy? I've been reading around on here and noticed a bit about cam belts and water pumps.
Cheers,