Does this product help?

[DZ1234]

http://www.ocztechnology.com/products/power_enhancement/ocz_enhanced_vga-hdd_power_lead

Does it really increase the power input to the video card, thus improving overclocking ability?

[Demo]

Not really sure but to me it only improves on the starting point it makes contact to.. your entire PSU wire system isnt like that so the moment it leaves those special cables i doubt there are any improvements

[DZ1234]

My PSU is also OCz brand (Modstream 520W). Should it work better with this cable?

[tdunks]

All it is is a shielded cable. Nothing special.