Full displacement boats tend to be stable but it depends on hull design
Some I have worked on roll horribly, but small ones tend not too.
Some ships can be go fast even though they are definatly displacement, one of mine did over 30 knots, but it had 25,000hp per shaft
very economic 4 tons of fuel per hour each shaft
Back too the tread
Really it is down to how far and how often compared to costs
If you like to stay inshore fishing most of the time, keep the nice boat you have but take a trip on other boats or charters when the urge to go further gets you.
If you want to go further every trip then a change of boat may be required.
As you say you suffer at sea, that may not be the best option.
Charlie