In low point games like your 750pt tournament a land speeder army can be extremely effective. Your opponent will not have much i the way of anti tank and so the multiple low armoured hulls can really save you from an all your eggs in one basket approach. They are also extremely versatile a major plus as you won't be able to build a decent specialized army at the points limit so it is always good to have multi tasking units. Another bonus here is that they are fast veichles, this really comes into its own against small forces as they will find it hard to catch and trap your sdpeeders, and as you have abolished the spearhead deployment half of your games will be Dawn of War so it really hhelps them get into the action. Anywys to compliment the speeders I would try and compliment it with a cheap HQ probrably a Librarian and some cheap Scouts as the Speeders can take up quite a few points. One last peice of advice, don't put your Speeders in compromising positions if at all possible, they are there to do the real damage and distract your opponent while the scouts do all of the real objective claiming, the longer your Speeders survive, the longer your Scouts survive, and the longer your Scouts survive the better your chances of winning the game. Anyways best of luck, and I look forward to hearing about how you did.