Motion at Sea
Given the two boats the Tartan 3700 should have a more comfortable motion and also be quite a bit faster. There are a number of factors that control motion comfort and a boat like the Tartan does well on most counts compared to the Pacific Seacraft.
The Tartan 3700 should have a substantially lower center of gravity and higher center of buoyancy. The Tartan should have a greater roll moment of inertia meaning a slower roll and since the roll axis is higher, should roll through a smaller arc as well. The Tartan''s deeper keel, and its keel and rig configuration should result in better dampening. Similarly the Tartan''s longer waterline should provide better dampening and mean less pitching as well. The Tartan''s finer bow should mean gentler impacts in a chop and a greatly reduced tendancy to hobby horse.
In other words the Tartan should have a substantially more comfortable motion.
As to speed, the Tartan should also substantially faster on all points of sail and in all conditions. The wider stern on the Tartan should give it more reserve stability (at the price of ultimate stability). The more efficient rig, and keel plus substanially higher stability should allow the Tartan to really exceed against the Pacific Seacraft upwind and because of its powerful stern, straight run, finer bow, and futher aft center of buoyancy the Tartan should walk away when reaching in moderate to high wind situations. The wider stern should permit the Tartan to surf better in a following sea and the finer bow and longer waterline should allow the Tartan to have better tracking than the Pacific Seacraft (except in extremely gusty conditions when the powerful stern sections on the Tartan would tend to generate a transient weather helm condition. In those conditions a helmsperson, an autopilot or a vane on the Tartan would need to steer more than on the Pacific Seacraft. I would expect this to be greatly offset by the lower helm loads on the Tartan.)
All of that said, these are two extremely different boats in terms of purpose, ease of handling, and accomodations. These are such extremely different boats that I cannot imagine a circumstance where a knowledgeable sailor would actually be making a decision between these two particular boats.