Let's face it, the 340 is not a sports car but I'm quite attached to it. It has an acceptable performance with a 1.7 if you make full use of the accelerator pedal :), just give yourself plenty of room for overtaking. One thing to watch out for is the tail end sliding away as you round a corner.
Motorway performance is adequate with a 100+mph possible although I don't recommend full throttle for extended periods of time. Fifth gear keeps the engine noise down but it's a bit sluggish going up inclines. It's quite comfortable at 75-85mph except for excessive wind noise from the door seals.
It drinks petrol. I can squeeze about 30mpg with gentle driving but I tend to drive it as fast as it'll go so 25mpg is more typical. The fuel tank is on the small side and only gives a range of about 220 miles.
If you like working on your car then you'll find that there is a fair amount of room in the engine bay. Most things can be reached easily, especially the spark plugs.
If you go to a Volvo dealer for servicing, be prepared to fork out a large wad of cash. Better to find yourself a good local mechanic.