RUNNINHORN you should make sure you take a look at Pantera, Active Thunder, PowerPlay, Sunsation, Superboat and Sutphen. As far as what you will need to run 70+ MPH a 454 Mag in a 24' Pantera or Superboat should put you there. If you get into a 28' boat with a single engine you should look for a HP-500 to comfortably get you into the low to mid 70's. And a 30-34'boat with twin 454's or 502's should get you mid to high 70's, some may get into 80MPH. All these boats are good, it all depends on what suits you, style, comfort, look, price, cockpit and cabin space ect. Superboat builds a 30' that they claim will run 74 MPH with a lab finished prob for $64,000 well built strong boat but limited on features. The 29' Formula is a nice boat, they are offering rebates and low finance they also come with a 5 year warranty on everything. The 32' Sunsation is also a very nice choice it will run low 70's with the Mercury 6.2's and high 70's with the 454 Mags.
Good luck, let us know what you decide on