I've built a phase 90 with both sets, one I kept and the other was for a customer. To me they really sound very similar, and isn't massively noticeable unless you're looking for it. I found the 2n5457's to be easier to dial in, and had a wider range when setting them worth the trimmer, while the 2n5952's we in the spot or not.
Both sound warm and phas-o-licious. Btw, the only reason I sold the one with 2n5456's was I was waiting for an order of 2n5952's to show up, cause I didn't have a matched quad, and wanted to get the phaser to the customer. Fired right up and sounded amazing, and compared it to mine before sending it off. Again, unless you really look for differences I don't think you'll notice any difference.