Hi Robb
There were some performance comparisons posted here earlier in the year. IIRC the running totals update did a million rows in about 6 seconds, the rCTE method took a little less than twice that.
For fast, accurate and documented assistance in answering your questions, please read this article.
Understanding and using APPLY, (I) and (II) Paul White
Hidden RBAR: Triangular Joins / The "Numbers" or "Tally" Table: What it is and how it replaces a loop Jeff Moden