I've had an optima red top on my machine for the past five months. Saw me through the winter fun with no problems, using all the electrics a lot didn't seem to phase the thing at all. Got mine from Frog Island 4x4 when they had a sale on for £125.
Not sure if the early models are the same (mine's a 2006 facelift TD4) but I had to mod my battery tray slightly and lengthen the cable to allow it to fit tho' (Piccy available if you neeed it)
Steve