@George4Tacks and @BobKamman:

Thanks for the feedback.  All points well taken.

Due to the UCE , I'm filing more MFS returns in one year than the past ten, perhaps 20. 

In the filing I'm working on, Husband's MFS return will have a balance (in October! - think penalties, yikes) and the W's a refund.  The overall tax saving is over $5K, and unless I'm sure it's a sure thing to get the split, I agree with George that I should NOT rely on the IRS to do the sharing of the 1040ES paid by the Wife.  Paying the penalty would be better than dealing with two CP24's...

Lacerte's MFS splitting function makes the job quite easier.  I've found it very handy.

Thanks for your input.