Topic: QA time through the SDLC

Just for give you a quick response, the following is my stats overview:

. QA-Small Project: less than 2% of total effort.
. QA-Medium/Big: 2 to 3% of total effort.

QA is not Testing:

. System/Acceptance Testing effort: 7 to 20% of total effort.
. System/Acceptance Testing mean duration: 4 weeks.
. Stress Test duration: 5 to 7 weeks (time box).

Finally, QA activities impacts in QA effort estimation. First of all, you must to know wich QA activities you'll develop and who'll the participants. These activities may be permanent or by deriverables.