In GT4, the S2000 LM would completely walk the Spoon S2000 because the latter was heavily glitched. In GT5 they have fixed the glitch so other than the S2000LM having a few more pound feet of torque, they drive pretty close to identical, with the LM being the tiniest bit faster. Both have very neutral and very stable handling.
I actually did a race Sunday night where I was using the Sppon and someone else was using the LM. Our qualifying lap times were only 2 tenths of a second different (with the Spoon being slower) over a 2 minute long Toscana track. It would really come down to the drive more than anything else, so you might as well just pick the one you like the looks or sound of more.