After two years on Honda Waves my Kawa Boss 175 feels like a real bike! Everything is massive and has a big bike feel to it. The engine revs to what seems like 8000rpm, top speed is between 110 and 120km/h, and it's easy on gas. I've had lots of bikes over 750cc, including a 1400 Intruder, but for Thailand I'd say that's overkill (even though if I'd win the lotterie I'd buy one!). The 200cc Phantom is all you need around here, from puttering around town to visa runs to the border. I can recommend those things - never thought they'd be so much fun!
P.S.: If you're tall, try the "smaller" Kawa - the footpegs are more forward, it feels roomier.