I used to be a Internet explorer user but switched to Firefox just 3-4 months ago. For me a browser should be able to open most commonly used websites on the web and supported by third parties like flash, JAVA etc. I never did speed tests and never bothered about them. Never bothered with security issue either as I always had a updated Norton to protect me, never got infected either. Even though firefox was around with its impressive add-ons I just did not feel a real need to switch. The thing that forced me to switch was that Norton stopped add blocking feature in its products. They just removed it from their new line. Norton add block was the only tool good enough for me to block adds in Internet explorer. So, I switched to firefox. I now use fire fox with Internet explorer theme (vista-aero), It looks exactly like internet explorer 7 but has firefox running under the hood with its addblock plus.
So, for me internet explorer v8 is no go as it does not have add blocking.