What are your thoughts? How do they compare purely on sailing characteristics? Which one would be the fastest, the most stable? How significant is outboard vs. inboard? Any potential problems to look out for, weak areas?
They are 3 comparable boats, all suitable for your purposes, although few people actively campaign these boats racing in PHRF. If you are really interested in racing in S.F. Bay area, I would try to find a planing keel boat, such as an Olson 30, Hobie 33, Santa Cruz 27, Moore 24, J/27, J/29, etc., for double or triple the cost.
How do they compare on sailing characteristics? Which one would be the fastest, the most stable?
Research the PHRF ratings in your area for relative speed. There is not a whole lot of difference between the boats - I see the P28-1 at 198 and the I28 at 201 in Northern Calif., the Cal 27-2 rates 207 in N.E. PHRF, where the P28-1 rates 195.
How significant is inboard?
On boats this size and displacement, very significant. An outboard propeller will struggle to stay in the water in any kind of waves on a moderate displacement 28 foot boat. You should look for a diesel, if possible. Don't buy a boat without a working engine.
Any potential problems?
You need to research each boat to discover the common problem areas and pay particular attention on your own pre-contract inspection to those problem areas.
I enjoy my Pearson 28-1 and would encourage you to view my 20 videos on youtube at jameswilson29 channel to see its sailing characteristics for yourself: