A friend of mine has a 1987. When new it did 30kts and cruised at 22kts. These days with a lot of cruising gear,tender and at least 3 kitchen sinks he tops out at 26kts with cruising of 16 to 18kts. He is perfectly happy with the boat which he uses for a combination of coastal and river work (last year we did 500miles in a week Solent-Poole-Channel Islands-Cherbourg and back to the Solent and it coped with no problems)For more info his boat was featured in a test of time in MBM about 12 months ago.Hope this helps.
I think the boat you are refering to has a Volvo 171 not a 146, the artical said it needed a special technique to get on the plane, where the wife went forward until the boat was planing , then returned to the cockpit. I think a 218 with a Volvo 146 will be struggling to get on the plane at all if heavily laden.
I would keep looking for one with a bigger engine, unless you intend to trail the boat,a smaller engine will make the boat lighter. Or if you intend to use it on rivers a lot, where the power is not important.