Can I throw my 2 cents worth in here too
1/ You get what you pay for with small diesel engines. Try and get a machine with a "Yanmar" engine, not neccessarily a Yanmar machine, they are renowned as being the best small diesel engines
2/ Bigger hp rating isn't a true guide, small bobcats are generally around 30/35 hp and a 5 ton excavator will be 30/40 hp it's all in the hydraulics and pumps.
3/ 3 point linkage back hoe attachments will dig ok, BUT they are an absolute pain in the bum to attach and remove ( I had 1 for 7 years )
4/ Just get experienced contractors to do the bulk of the work for you, they will do more in a day than you will in a week, they have to maintain the machinery, have the insurances if they dig up the local Telstra cable etc.
5/ If you really want to get a versatile machine try looking at a 2nd hand,low hours "positrack" bobcat ( the one on rubber tracks). Controls are very easy to use,( all hand, no foot pedals, very intuitive ) no flat tyres, almost unboggable, and a huge range of attachments are available
My qualifications for these views...............30 years digging holes and filling them in with this type of machinery