VFM is a difficult term and changes with every individual.
Let us assume that we are in the market for an apartment. Some want maximum area while some want to live in premium locality (maybe smaller area) for the same price. Extending the argument to cars, some would prefer no-frills/high economy/low maintenance cars while others may choose better features/looks/style, etc.
Coming to your requirements, since you have the budget, the 46HX850 is within your grasp. The 46EX650 is much cheaper. Do you watch a lot of BDs and/or DVDs? Then HX850 should be your choice. Else EX650 is good enough. As far as lifetime is considered, nothing can be guaranteed but both should last equally well.
I believe that you could also add 46HX750 as a choice that is a bridge between the two.