Hi MTT - Tough spot to be in, picking between these two models
Both are great coaches, and both will meet your stated needs. On the power front, Essex did have the ISX as an option, but I don't recall if the 2007 had this or not. I think the Big Cat and the ISM are both going do you well on the power front. And of course, you said you had big truck experience, so you can do your own 'chevy vs ford' between them...
The handling and ride between these two will be different, the the Spartan K2, I think, is in the Essex, and it has a solid fan club. The Dynomax is a different feel then the Spartan, and is equally a fine chassis. So the ride comes down to what feels right for you.
Bob and Mr D - I doubt Bo was trying to slam Newmar, as this is not his board style... IMO, at the Essex to Magna levels, they both are great quality coaches, approaching build and finish with an eye to detail. I do agree with Bob's comment about the 2007's Magna having a very a bit higher rating then the Essex, but I honestly don't consider them direct competitors. I think the Essex slots in just a tad above the Magna, while the next one down being the Moutain Aire slots just a bit down below the Magna. I see the Affinity as just a tad above the Essex. BUT, all subject to opinions. Both CC and Newmar have different level models, and nothing wrong with this. Newmar also has a line of gas Class A's, and 5th's too. So it really comes down to a model by model comparison, IMO.
As these models don't seem to line up directly - very hard to do an exact comparison... And it does not really matter we think, it is what the OP thinks is important to him.
Between these two, I would road test for driving feel, check condition, and most important - how does the coach support my living needs and likes... Just can't go wrong with either of these.
If the Essex did have an ISX option, I would see if the extra power over the ISM or Big Cat was a selling point. Only the OP can determine that...
Have fun, and please let us know what you end up with... Foretravel also makes a ncie rig, and have ample power options, if you have not checked into those... The Executive's from Monaco have a big block option too... And Travel Supreme did too. Soo many nice coaches
Best of luck,