Not too sure about PCSX2 but Dolphin will run fine. Haswell is quite a bit faster (25% per clock) than Sandy Bridge, as seen in the Wind Waker benchmark thread at the Dolphin forums.
To get full speed on the most demanding games like Super Mario Galaxy and Xenoblade however, you will need to overclock to 4.2 Ghz or better. Expect CPU requirements to continue rising as the emulator becomes more accurate (thus slower with less speed hacks). Thus the 3.5 stable build might be faster for you than the new 4.0 build.