I will be more helpful.
It depends what you want out of the car.
Both will offer that amazing V6 noise, and give you real grunt and low down torque you get from a proper N/A monster. The Mk4 is a slightly simpler beast, and is less likely to cost the earth in repairs.
The Mk5 is obviously newer, so a more modern interior and exterior styling (I prefer the look of the mk5), but is probably more likely to cost in case of repair. Bear in mind, that alot of parts of the mk4 R32 are interchangable with the v6 lump in the 4mo and to an extent mk3/Corrado VR6s too. (Mechanical mostly not electrical though). The mk5 less so, although still quite a bit tbf. Its entirely your choice, and I'd wait to see what you are likely to have cash wise before deciding, as the lpg is gonna cost you around 1k too.
I absolutely agree with you though, 4 pot tfsi will never offer the noise and excitement when you plant your foot, even with a remap! Turbo torque just doesn't compare with unadulterated N/A back breaking torque. I should be getting my accident compo around Feb (finally) so I've been looking at buying a non running Corrado VR dropping an R32 in it.
