Do you think saline will look and feel fake when going from small A to large C and with breasts initially already far apart? (Ph

Hello,
If you have to wait then do so.  You would benefit from a highly cohesive silicone gel implant to minimize your risk of visible rippling. Best of luck!

It is important for patients to understand that augmentation will "augment" all aspects of your anatomy. The spacing of the footprints of the breast on the chest wall will vary from one individual to the next. Widely spaced breast will appear more widely spaced and vice versa. 
The spacing (cleavage) is defined by the pocket. The pocket is defined by the plane of augmentation.When placed submuscular, the medial/middle limit is the sternal origin of the muscle. Wide sternum = greater separation of the breasts = less dramatic cleavage. This space can be narrowed (with some risk of symmastia) when the devices are placed subglandular or "over" the muscle. There is no muscle obstructing a medial push, however, there is a higher risk of over-dissection and mid-line migration of the implant (the dreaded "uni-boob").
With respect to your specific question, saline implants, in and of themselves, will not compromise your result. There is a less natural feel and a higher incidence of rippling (as compared to silicone). However, none of these factors will affect your cleavage/spacing. Cleavage is defined by anatomy (as described above). The question of "fake vs. natural" is typically a function of staying within the footprint (BWD) of your native breast.
As always, discuss your concerns with a board certified plastic surgeon (ABPS).