Mick,
Yes it will be quick, but unless you're under 80kgs you'll need 25knots+.
I've got a RS-slalom 5.4. I'm 90 kgs and only used it 5 times in the last 12 months.

I got $300 trade in on an RS-4, 6.7 that was in good nick, so the asking price is a bit high.
Although the owner probably spent close to $2k on them new, he/she should be happy with approx. $800 for both.

I got the new RS-Slalom MkII and it rotates freely and easily, (you don't even need to pump the sail !!)

That's my opinion, have fun.