well i've lookd at both options and sofar the turbo seams to be the slightly cheaper option and for the price it seams to give the better bhp/Ԛ£
obviously the both have the advantages and you could make the conversion as cheap or as expensive as you want depending on want you wanted to do.
2.1
cams Ԛ£300
megas quirt Ԛ£300+ setup or DIY
pistons Ԛ£500-Ԛ£550
M44/320d crank Ԛ£Ã”šÃ‚£Ãƒ”šÃ‚£Ãƒ”šÃ‚£Ãƒ”šÃ‚£
Throttle boddies
block bored out
170-185 bhp???
turbo (still looking at prices)
Turbo
volvo intercooler
Solid exhaust valves
megasquirt
Around 200bhp?
i still havent decided between the 2.1 or turbo but the turbo is starting to look more likely + turbos got room for expantion in the future.

You should never underestimate the predictability of stupidity
M42 Supercharged 285bhp + M3 6speed box