V40 petrol variants
 

How good an engine is the Ford derived T4? How does it compare to the T2, 3 and 5 in terms of reliability?

The T2 and 3 are basically same engine with a different engine map on ecu,

The T5 is a 5 pot Volvo engine,

As of 2015 model year there all 4 pot Volvo engines,

There isn't that many petrol engine Volvo's about but the ones that are don't seem to cause many issues, odd boost pressure sensor that's about it

My friend has a v40 T4 with polestar added. No issues other than a recall on an exhaust gasket. Goes very well and isn't to bad on fuel considering it's got 200bhp!

you got 200 bhp as standard on a 1998 V40 T4 :-)

And a proper true volvo engine an all!!

Yes but you can bet it wasn't as fuel efficient! :)