You will be fine to mix those fans since they are of comparable rpm ranges (1150rpm / 1200rpm)
You will definitely see some improvement in performance with push pull than you would with just one set of fans and you might even be better off with mixing the fans than you would if they were all the same type. For example, here's Martin (of MartinsLiquidLab):
Originally Posted by Martinm210
Absolutely, I encourage mixing of fans and have done it many times. The mixing fan phobia generate by forum members is really just another forum myth by users not knowing. I have yet to see any testing to show it being a problem. Actually I have found mixing two different fans to be a benefit at times. When testing the H220 I found two AP15s plus two Helix to be a great match. The helix alone seemed to have a little harmonic under pressure in push only that goes away and smooths out when the GTs were added. Also anytime you mix like fan speeds you can get rpm harmonics so having fans at speeds that are a few hundred off is a good thing.
Noctua even does mixing of fans and speeds on their NH-D14.
While it may not make sense to mix 5000rpm Deltas with 1200rpm yates, I sure wouldn't worry about 500rpm differences particularly when resistance like a radiator is keeping air flows well below either fans max air flow rate. Mixing fans is a good thing..