For CPMG, the maximum kex should be 10^4, and for R1rho it should be 10^5.
This is altered from the value of 10^6.
The suggested restraints for 'kex' follows from article, on page 224:
Nuclear Magnetic Resonance Methods for Quantifying Microsecond-to-Millisecond Motions in Biological Macromolecules.
Palmer-III, Arthur G., Kroenke, Christopher D., Loria, J. Patrick
Nucl. Magn. Reson. Biol. Macromol. B, 2001, Vol: 339, pages 204-238.
U{DOI: 10.1016/S0076-6879(01)39315-1<http://dx.doi.org/10.1016/S0076-6879%2801%2939315-1>}
