Assuming two boats in equal material condition, consider the following:
Ballast to displacement ratio: 35.5%
Sail area to displacement ratio: 14.5%
Ballast to displacement ratio: 40.75%
Sail area to displacement ratio: 16.75%
The Seafarer will be more tender (tippy), and the Pearson will be a little stiffer.
The Pearson has the higher SA: Displacement ratio, while being only 200lbs heavier, and so should be a little quicker.
The Pearson's waterline length is a hair shorter, but I'm not sure if this will really slow her down compared to the Seafarer.
The Pearson is a tad beamier, which might give you a little more cabin volume.
The cabin layouts are very similar, so no clear victory there.
I give the performance edge to the Pearson, possibly the edge in comfort.
I give the maintenance edge to the Seafarer, with it's encapsulated ballast and skeg-hung rudder.
On the Pearson 30, the ballast is encapsulated like the Seafarer. I believe that the ballast on the P26 is cast-iron and bolted on.
I would carefully inspect both boats. If the bilge sump of the P26 is clean and dry, and the keel bolts are in great condition, I would buy the P26 for the performance edge.
If the keel bolts are suspect, I'd buy the Seafarer, all other things being equal.
If these boats are in the Maryland Chesapeake area, I'd be willing to take a look at them with you.
Just remember- My opinion is worth exactly what you paid for it.