I recently went through the research stage of comparing tillerpilots for my Cheoy Lee Offshore 27. The Raytheon ST1000 should probably be considered only for small daysailer types and powerboats. The additional features and power of the ST2000 are well worth the extra money for a boat your size. Practical Sailor did a comparison of the ST2000 with the Simrad TP30(used to be Navico). They are very similar, and PS conclusion was basically a tie with a nod to the Simrad unit for slightly less amperage used. As far as size of the unit vs your boat size, opt for a unit that is more powerful than the minimum recommendation. You will want a unit that will hold a course in nasty conditions while you go forward to change a
jib or whatever. If you can find a factory reconditioned unit you will save good money.