"Faster moving" being relative to our assault mechs, which isn't hard. Dervishes, Trebuchets, and Catapults are all relatively fast mechs with good long-range support ability.
Weight class =/= what you boys are asking for, methinks. I just did a little fast romp through sarna.net for these three 'Mechs, to double check.
The Trebuchet and Dervish both weigh in on the heavy end of the medium range, at 50 and 55 tons, respectively.
The Catapult is a heavy, at 65 tons - and not the most useful option of the three, looking at it.
So, yah... at this point, I've been as helpful as I'm gonna be, I'll leave you boys to it.
I will say this though. I really don't like watching people tell others what to play, and you guys are starting to toe that line pretty seriously. I realise advice was asked, but this is starting to make me really twitchy. >.<