The lamp ratings by the manufacturers don't mean anything, but I will say the Pro8200 lamps are more likely to last longer than the hd20's, simply because the brighter a lamp starts out the longer it will probably last (as a general rule it will maintain its brightness longer). The hd20 is only about half as bright as the Viewsonic, but if you are going to be in a controlled lighting environment, you'd be hard-pressed to beat the gaming on a Mits hc4000. I'm sorry but 1080p on the Mits in a game beats 720p easily (especially for PC games), 1080p is more natural looking and less edgy.
The lag measurements I've seen on the Pro8200 were some of the lowest I've ever seen on any projector, around 15ms. That said, I cannot vouch for their accuracy but I've never heard a single person having seen any lag on it. I own the Pro8200 and a JVC, the only issue the Pro8200 has is the 1:1 pixel mapping issue. The Pro8200 doesn't need a game mode because it is using a simple pixelworks processor and is only a 60hz projector, which is one reason it probably has so little lag (not a lot of fancy processing going on).