Greg, Since everyone's definition of high volume differs possibly knowing how often or with what regularity you plan on printing B&W would be of more assistance in guessing a printer choice.
For me, instead of outlaying the money on a separate printer or going through the hassle and expense of changing out blacks, I resorted to using a commercial lab specifically for my B&W printing needs. I never have had to wait longer than the day after next to receive my orders and have not been disappointed with the results. I gave up immediacy but gained not having the expense of amortizing another printer in my per print cost.
Not a direct answer to your question, but it is an alternative solution if you are not printing separate Black and Whites every day.