nearly all bowriders above 20' have a V8.
as for speed, most big-block powered boats are 50-60mph boats. how fast do you want to go?
with or without a head / changing room?
with 10 adults on board, you may be looking more at a Sundeck style boat (larger open bow area, front boarding ladder). definitely in the 28-35' range
guessing your budget is about $30k
something like a Formula 280 Bowrider or a SeaRay 280 BR or a Cobalt 282
get the 8.1 or 8.2 motor.