Nigel,
We looked at the 155 for our operation which is probably completely different from yours of course and came up with the following:
Pro
Speed
Range
Quiet
Good visibility
Volume
Flat floor
Sliding rear doors
Huge luggage space
At the moment if you know where to look - cheap
Cons
Hover performance
OEI performance
Engine power degradation over time
CAT A vertical profile - none
Altitude performance
Empty weight
Air conditioning
I guess you have to assess your priorities.
The hover performance seems to be a trade with speed. Comes from tacking another blade on what was once a 4 blade rotor. MGW ISA OGE = 0.
OEI - see above. OEI MGW ISA +20 200fpm/80knots = 150 ft/nm???????? Curve of the earth even before your authorities have attacked it!
The Arriel 2C1/2 struggles to make power sometimes and you can be splitting hairs. Seems 350B3 operators can have similar problems. No doubt it will be addressed and nobody said when.
CAT A vertical profile. I am told it is a legacy from the 365 gear. It can't handle the increased gross weight by design. This seems plague a few designs that are growth variants. (A109 Power?)
We regularly operate and land at over 10,000'. Performance up there is pretty limited. They were slowly expanding the envelope and maybe it will go further and in fact the certification trials occurred in exactly the same area. I think it is a lot better now.
It is real easy to eat your payload with EEW increases. Check your figures closely. Don't know why in this day of micro electronics people fit radios out of a 747.
Air conditioning performance seems to be not as good as it could be and may never be.
In your patch if the question is Payload/Range/Speed, it may be worth looking at because some fairly impressive numbers can be achieved. 160 knots should be easy.
Price - if you were to look really hard you may find a deal. You just have to consider why!
If the Hover performance or CAT A vertical is not acceptable. The N3 is probably an option if you can find one of course.