The Dauphin is a good helicopter for medium range SPIFR. It is reliable and cheap to maintain. The cruise speed would depend on what part of the world you would be operating and what weight you wanted to operate it at (N. Europe around 140 knots, tropics around 130 knots realistically speaking).
Shell have been having some problems with their EC 155s in Nigeria. From what I hear a lot of them are no different from the teething problems almost any new type has in its early days. The main complaint is probably to do with actual single-engine performance as opposed to claimed single-engine performance. The Arriel 2C1 is basically pretty much the same engine as the Arriel 2S1 as fitted in the S76C+ and most operators of the latter type in hot climates have been having a lot of problems with engines failing power assurance. Supposedly the Arriel 2C2/2S2 will address most of these problems, but that remains to be seen.
I've yet to fly a helicopter that doesn't leak in the rain.