I have had the pleasure of working at Dyfed-Powys albeit on both the AS 355 (not their old 'N') and the trusty old Bollock!!
From this I appreciated that the unit had a huge area to cover and probably placed speed in transit at a higher priority than possibly other units did - so hence the 109.
I would suggest that the Ec 135 and the MD 902 have to work very hard to get close to a 109 - but what the hell do I know!!
I don't fly the A 109E, but I know a man who did and I may ask him to comment for the benefit of those who want a pilot's eye view when comparing the 902/135 and 109