I doubt the GT 740 doesnt require a 6 pin connector. On most places I see, it needs one. So a PSU is must in this case. Therefore, the R7 250 wins.
PS - Get the HD7770. I can see a fantastic deal on flipkart for it for 7144 only. An HD7770 kicks the GT740 and R7 250's butt! You'll need a 6 pin connector for it though and since FK has 10% off if you use an SBI credit/debit card you could get the GPU for 6430 and an H81 motherboard for 3000. Win-Win situation!
Great deal! but existing PSU has 20+4=24 pin connector, just now confirmed by Technician.
I'm in last rush, badly needed to finish by ordering today. Can't bear more son's apprehensions since last 15 days! pl support to order today itself. I'm ok with +or- 1 or 2k here or there!