It would be slower. A jet drive is about 60% efficient compared to a normal stern drive or outboard configuration. Power is lost mainly by converting helical thrust into linear thrust by passing it through stator vanes. Jets are also heavier, louder, vibrate more and are more expensive. However, they have one overriding advantage: they allow you to go places you wouldn't normally be able to reach. For example:
Much slower and much less economical - to illustrate:
I have a 6.8 m delta which had a hamilton jet and a 230 hp inboard yanmar which had max speed of 30 knots and cruising at 23kts on 25-26 lph. It has been converted to a 250hp suzuki outboard and now having top speed of 46 knots and cruising at about 32 knots on 19 lph.