When paying the extension of time fee via EFS-Web, do I need to attach the petition for extension of time?

No, the submission of the fee set forth in § 1.17(a) will be treated as a constructive petition for an extension of time in any concurrent reply requiring a petition for an extension of time under 37 CFR 1.136(a) for its timely submission. The Office, however, strongly recommends including a petition to avoid potential delays in processing. See MPEP 710.02(e).

USPTO FAQ - Questions and Answers (30NOV2007)