The recommended DDR3 mem clocks are 1800MHz for the GT610 and 1600MHz for the 6450. But both the GT610 and the 6450 being sold in India are using much lower mem clock speeds of ~1000MHz or so. So toss a coin or pick whichever one has better mem clocks Probably the 6450 since it has lower power consumption too.
Thank you so much guys! Got the 6450. The clock speeds were the same on both. I went for the one with the longer warranty since thats the only need right now.