You'll be fine with a 4wt on that rod. In fact, you might even find it a little easier to cast than a 3wt.
Incidentally, unless there's a specific line you had in mind from your local shop, I'd recommend you have a look at the lines offered by
Pitsford Pirate on this forum (and many others too, for that matter). I've had several lines from him over the past few years and they've been excellent quality and outstanding value for money. (On the other hand, supporting your local shop is a good thing too…)