Believe me, this card is much better than your old card as well as the 7750.
In fact is is actually two levels above the 7750.
7790 > 7770 Ghz Edition > 7770 > 7750
So you can see there is quite a bit difference. The comparison between the 7790 and the 7750 is :
I was not able to get the benchmarks of the 2400XT anywhere but believe me, the 7790 is like 20 times faster than that old card and is like 4-5 generations newer and much higher ranked (400 of the 2400
vs 790 of the 7790) so it should perform much better.
Also Can I know the specs of your PC just to ensure that there is no bottleneck. Tell me these specs :
1. Case
2. CPU
3. PSU
4. Motherboard
This should ensure the compatibility.