I think it's sufficient. I used to be reluctant to spend more, though I think I'd put my limit around £250. I understand not wanting to spend more than is necessary (I'm the same) and monitors aren't the easiest thing to know how much is necessary - not like it can all be boiled down into a benchmark result like a GPU or CPU.
I think we have the same priorities anyway - quality first (so IPS or PLS), and then as fast response as possible without compromising quality. Almost all manufacturers implement something called RTC overdrive, which accelerates high contrast pixel switching by applying increased voltage to those pixels.
Problem is, apply too much voltage and you get something called "overshoot" where the trails are simply inverted so instead of a dark object leaving dark trails, it leaves light trails (and vice versa). Most manufacturers either apply a little too much or not quite enough (I think it's impossible for them to get a perfect voltage since the panels themselves vary - they don't all come off the production line exactly the same).
So best solution is an overdrive impulse you can adjust manually. Some manufacturers give a choice of off/medium/high (or words to that effect - they call it 'Premium', 'Advanced' etc) and others are just on/off. Some aren't even on/off, just always on. If you buy from ASUS or Iiyama, you get six or five settings respectively, so you can a nice balanced overdrive voltage around the middle. If you buy an ASUS (VS239H-P is cheap) then set Trace Free at 40. If you buy an Iiyama (ProLite XB2380HS is another option) set Overdrive at 0 (goes from -2 to +2).