Six inch rods will not result in any more torque. If you design an engine with the correct cam timing events to take advantage of the long rods (longer dwell time at TDC), in combination with correct intake and header design, THEN you might see some slight gains. 3700# steet/street-strip/bracket car would probably still not realize much improvement in e.t. A light maximum-effort, high RPM, class racer MIGHT see a significant improvement with a properly engineered long rod motor, though.
EDIT: If you are building the engine from scratch and have not already purchased pistons and rods, then by all means go with the 6 inch rods. The cost of the pistons and rods should be the same, or close to, the cost of the 5.7" pieces. Tell your cam manufacturer to recommend a cam to go with the longer rods.
[ February 07, 2003: Message edited by: engineguy ]</p>