I can speak from first hand experience. I have both the BCZ2640S and BCZ3060T Max Torque and I bought them this year. We like them both but the 3060T has so much more balls. The guys and I are thinking it uses less string for some reason as well. Either way, the weight difference between the two is insignificant-the difference in power though-whew! We fight over who gets the 3060T. On the other hand, I had a 6year old BCZ2640s or that we loved more than the brand new BCZ2640S-but that was mainly because the older one had the guard modified (Mom ran it over). It let us run the string a bit longer.
My back up-back up trimmer for the guys is a Stihl 90R Kombi. Lots of torque but the guard doesn't allow you to use much string. Its slow as hell. On the plus side though, its great with the chainsaw and hedge trimmer attachments.
If you're doing crazy clearings spend the extra $50. I had no other option at the time-they didn't have the BCZ2640S I wanted so I rolled the dice and went bigger. No regrets at all and no fuel pump issues on either machine as of yet. I'll use a brush saw at some point this season and when I do I'll post up a review.
Good luck in your decision!