Heat pump questions

[jrj701]

I am installing a small inground pool (14,000 gal) with a 600 gal spill over spa. I plan to go with a Hayward heat pump, and was wondering if you can oversize a heat pump? According to some calculators I have seen, a 80,000 BTU will suffice, but the Hayward 81,000 btu unit is manual thermostat and only has a pool mode, whereas the next size up 118,000 btu has a dual pool/spa mode. Don't know if i need that, although it may have seperate pool and spa temperature settings to avoid having to change the therostat if you just want to heat the spa. Basicly wondering if oversizing will cut the efficiency.