You can apply for an extension of your H1B anytime after July 31, 2007. I highly recommend that you do that in Aug. itself. so that you will have an extension till Jan 31, 2009.
If you want to take a 3 yrs extension then you can wait for your LC to get cleared from BEC. Once LC is cleared then apply for I140 under premium processing which might take approx 1 month or so to get cleared (based on what I read from this forum members). After getting I140 cleared if you apply for H1b extension, you will get 3 yrs extension (till 2011). But this will be risky.
The best thing to do is get an 1 yrs extension based on your current LC pending application at BEC and then once you get LC cleared go for concurrent I140 and I485 if your priority date if current, if not then go for PP I140 and wait for I485, in the meantime due to visa retrogression if you cannot apply for I485 then based on LC & I140 clearance you can apply for 3 yr. H1b extension.
Sorry for the long reply.