Very knowledgeable, experienced slant-6ers such as Doug Dutra have built up high-perf 198s and found that they run like…198s. Especially with your 5500-foot altitude taking a bigger-than-16% bite out of your performance (3% per thousand feet above sea level) and today's alcohol-contaminated gasoline with its lower energy content, you're better not to skip out on displacement unless you are trying to build a max-MPG motor, which is not what it sounds like you're doing. The difference between a 198 and a 225 is the connecting rods and the crankshaft. Everything else is the same. The conrods are a hot-ticket item for building a long-rod 225 (225 crank, 198 rods, 2.2/2.5 turbo pistons with high pin location to allow the long rod to work with the long-throw crank).
