I have had a Tsunami 145 for a few years, and this year added a 175 Pro to my collection of boats. I love both of the boats.
I have taken the 145 on two full 7-day trips and numerous 4-5 day trips. Rivers and Lake Superior included. I am large, at 6'2" and 270lbs. I fit very comfortable in the larger-bodied Tsunami, but I did move the seats back about 2" (one hole) to make entry/exit easier & to accommodate my legs. The 145 on a weeklong trip along Pictured Rocks National Lakeshore on Lake Superior handled beautifuly in 3-4' swells, but loaded with my big butt and a week's worth of gear, the 145 was riding pretty low in the water. Thus came the convenient excuse to step up to a 175. I could load two weeks worth of gear and food in it & still have no problems paddling it. The 175 is too long for a river float, so I have kept my 145 as well. When my boys & I paddle, speed is not a concern. If we do 10-15mi a day we're fine. So, I can't really attest to whether the Tsunami is a fast boat, but it paddles easily.