Certification Question- IGI vs GIA

I’m looking at buying two loose diamonds (1.4 cwt x 2) to have a jeweler make into studs. My specs are excellent (near highest) grades in cut, color and clarity. I’ve identified some nice stones on loosegrowndiamonds.com. When searching for certification, IGI doesn’t seem to change the price, but GIA certified are almost twice as expensive. The underlying question is, can I expect the diamonds to meet their advertised specifications with an IGI certification? Also, any ‘better way’ suggestions would also be appreciated.