The wires will easily reach, no problems there.
As for the monitor, getting a Crossfire setup to play games at 1440x900 is really not worth it, since at that res, a single HD 4850 would be more than enough to run any game completely maxed out (except Crysis of course, but that's the case with most other cards in the same price range). So unless you get a monitor capable of at least 1600x1200, there's no point of getting two HD 4850s.