Hi Larry,
For our CLPA purposes we need to move up from a 14.8V battery to an 18.5 battery when our planes start to get over 65 oz. and over 650 sq in and/or really thick wings. This is the normal way to get the added power needed for a larger mission. (we do this all the time in ERC)
More Volts = More power .... as others have wisely said: "IF the motor/ESC is designed to take it and with the correct KV/prop for the mission".
My P-47 looks like it will be around 69+/- oz (scale stuff added ;-) with a 680 sq in medium thick wing and lots of big fuselage drag. I never considered using less than an 18.5V battery to power the Plentenberg Orbit 25. This is the same power system used by Paul Walker. Bob also used 18.5V in his T-Rex after finding out that 14.8V was not giving enough power to fly a good pattern.
I use an 8S, 29.6V battery in my 2 meter size Yak-54 at 9 lbs. This works well. :-)
Our medium size (25 lb) IMAC ERC planes use 44.4V 10,000 mAh batteries. (4 batteries to get this)
YOUR NEW PLANE:
If that beautiful new take-apart plane of yours is going to be more than 60 oz. you may want to go with a 5S 18.5V battery. ..... I like Dave and Paul's philosophy: "more power helps a lot!" ;-)
Thunder power just reduced most of their battery prices by 25%, they make great batteries and now they are a very good value. ..... But I have switched to the excellent Hyperion batteries. They are perfect for CLPA. They have 4 times the duty cycle of other batteries, they use a new type of construction and high quality materials that allow a safe 5C charge rate using a balancer during charge (I'm not brave enough to use 5C but I do use 3C and get full Charge in <20 min. :-). These Hyperion batteries only cost $128 for a 5S and only $103 for the 4S. They are also the perfect shape for our use. .... I would still use them even if they cost more than the TP batteries.
Regards,