We had to make the same decision in 2014 but it was Dutch Star 4018 vs Ventana 4037 (same layouts). Both were on the lot at different dealers. We did fairly long test drives on both units including some pretty rough side roads. I couldn't discern the difference between the independent front suspension on the DS and the straight axle on the VTDP. I also couldn't see any more pep in the 450 HP DS than the 400 in the Ventana. The side rad on the DS cuts into storage space but does certainly offer easier access to the engine compartment.
We would certainly be happier with automatic slide arms and, in the current year's models, the carpet-free slide-outs.
We are very happy with the Ventana and happily spending the $30k we saved. (Units were not identically equipped, option-wise)
2014 Newmar Ventana 4037
2016 GMC Canyon SLT - Crew cab, long box