I know your boat and am currently cruising with a CPT aboard a Pearson 424 Ketch of comparable displacement (tho'' with an extended fin & skeg hung rudder vs. your full keel).
CPT a/p''s do NOT use lots of amps; quite the opposite, in fact. We estimate perhaps 3 amp/hrs. Of course, this is immeasureably dependent on how the boat is trimmed & how responsive your boat is. CPT''s (when marketed by Charles Pukit in Ft. Lauderdale, and earlier by the inventor out in CA) have been used on far larger boats than ours, sometimes by delivery skippers who choose it because its powerful yet portable, and there''s no reason I know why it couldn''t handle your boat.
Having said that, here are a few things to mull...
1. It has no digital electronics (it''s an old tho'' reliable design) and so course corrections are delivered in ''jerks'' since it uses relays. Adjusting belt tension helps slightly with this, but its bothersome until you decide you will NOT be bothered by it! <g>
2. More concerning is the fact that, at modest amounts of weather helm, I''m finding the motor releases tension in one direction (but not the other), allowing the wheel to ''slip'' back from the position the a/p puts it in when on a port tack. It''s performing improperly, the Scanmar ''product manager'' (Keith) explained it was due to the Bosch motor needing to be replaced, then he was fired(!), and right now our unit is sitting on their test bench awaiting testing. Whether the problem is inherent in the design or due to a faulty unit, I don''t yet know. Were I considering the purchase of one, I''d talk with Gillian at Scanmar & explain that you''ve heard that a *very* few of these have disappointed owners due to ''slip'' and you want to be able to do a full install and then return it for a full refund if not satisfied. I think they''re understaffed re: technical capability but want to treat customers right and would readily agree to this.
3. Having said the above, this unit has been a HUGE help to us as we sailed and motored S & E from Florida to Trinidad. Despite its shortcomings, we''ve found it easy to live with (unlike the junk Navico product we''d previously tried to use) and perhaps the best gear choice after our Force 10 stove!
Let me know if you want more info; I''m calling tomorrow (Tues) a.m. to find out if I must accept an underperforming unit back, or am having a malfunctioning unit repaired.