Specialty Printer Application

I am not new to 3D printing and understand most of the technology quite well. Long story short, I need to build a printer for a specific application that must fit a few specifications. Keep in mind, cost is not an issue. I am not extruding plastic and actually need to build a specialty extruder, but this has already been decided. All I need to to figure out is what chassis to put this thing on.

- The application puts a fair amount of torsion and weight on the head. (Imagine a 4lb Bowden tube that does not bend nicely)

- MUST BE OPEN SOURCE (I have a RAMBo board/steppers/endstops at my disposal if need be)

- Speed is not a huge factor, 50 mm/s or less is enough.

- Accuracy and precision are huge however. I must be able to control both bed height and X Y accuracy very precisely.

- It should be about 200 x 200 x 200 in build size

- Finally, I would like to avoid moving the bed in either X or Y, but I may consider it.

I currently have a similar setup on a makerbot/ultimaker style printer. (The bed moves in the Z direction only, extruder on X and Y) I need to build a new setup for various reasons, and I want to explore my options. Mainly I am deciding between a Cartesian bot (makerbot/ultimaker style), a Delta bot, and an H-bot/Core-xy.

I have done a lot of research on all of the types, I just can't seem to determine the winner.

I know Delta WASP makes the Clay extrusion system (sorta similar to what I need) and they use the Delta bot. I would consider using this platform if it is deemed the right decision.

My questions are: What platform will give me the rigidity and accuracy I need? And even better, if there are any machines that meet these specifications, what are they?

Thank you,

Nick