I'll just give a quick overview of all the Le Mans cars in this game...most specifically all the cars that have their level at 23.
R10 TDI - Not quick enough.
R8 - Fastest of the lot.
R8 Team Oreca - I think somewhere in the middle...
McLaren F1 GTR - Good for its class but not against LMPs.
V12 LMR - Pretty fast.
Speed 8 - One of the fastest.
2J - Reasonable speed but looks like a washing machine.
GT by Citroën Concept - Lolwut.
Vertigo - Powerful, yes, but just not fast enough.
XJR-9 - Not enough downforce.
787B - Pretty reasonable allrounder.
Furai - Pretty sweet when modded.
CLK-LM - Alright speed, little outclassed though.
Sauber C9 - Great speed but a lot of tire wear.
GT-R Concept LM - Not worthy of Level 23.
R390 GT1 - Pretty good, but again outclassed by others. Plus the Road Car gets the same speed when fully modded and that's cheaper

R89C - Reasonable speed, middle of the pack perhaps.
R92CP - Very fast but again eats its tyres really fast.
Zonda R - Decent speed but not quite there.
Esperante - Just too slow.
Pescarolo '03 - Alright, but outclassed by the other two Peskys.
Pescarolo '04 - Much faster, good cornering, great at keeping its tyres right.
Pescarolo Hybride - Not too sure about this. Seems just a more powerful version of the '04 really.
905 - Superb cornering but suffers in a straight line.
908s - Both very good out of corners, very good all rounders.
Escudo - Lightning quick off the line but absolutely impossible to corner with.
GT-One - One of the fastest.
88C-V - Ridiculous speed levels and ridiculous tyre wear levels.
Toyota 7 - Decent out of corners but lousy down straights.
That should really give you all your answers