[Lil bastard]

First start with a budget. That will determine where you go. The 3.4 is the easiest and cheapest as I understand it, because you don't have to uprate the DME (at least that's what I understand). You're fortunate in that you are already setup for egas. The earlier cars require more work.

With the 3.6, you have to spend more on ancillaries, like a new DME. There is a company in the UK which can rebuild these things upwards of 3.7Ltrs. and I bet it's a screamer, but it ain't cheap. And I don't think any of them offer an additional 100Hp, though I may be wrong.

I think if it's done right, and documented fully (especially photodocumented), it won't have a detremental effect when you sell it, but I doubt it'd inflate the selling price very much. What it may do is sell the car faster.

But, any mod like this on a relatively plentiful production car can't be thought of in terms of a financial return. You'll get the return through improved power and that should be good enough. If it isn't, I might rethink the whole idea.