What is the surface area to volume (SA:V) ratio of a red blood cell?
I googled "surface area of a red blood cell" and this paper was the first result.  It should answer your first question. Though it was unclear to me what the surface area unit of measure was, which may require a bit further reading.  There's also this article, which goes a lot more into the math of calculating these two things.

As for your second question about how much it changes, intuitively I would guess very little and it probably does not significantly change exchange rates.  I couldn't find any research on the topic.  The hard part is defining all the shapes they may get squeezed into, then either calculating or measuring SA:V. Possible?  Surely, a well written computer model could do it at some point.  But worth the time/money?  Probably not.