Should be about £400 for an Iiyama 144 Hz
Yes but it's not in the same league as something like an M27Q, GL850 or MAG274QRF-QD.
For one, the input response time of the iiyama is known to be ~20ms (vs ~3ms on those above). As for the pixel response times, there are no reviews from people like RTINGS, and the most I've been able to find out is that the panel is made by BOE, a large Chinese panel manufacturer with their own IPS-type tech called ADS.
If you want something with proven (and reviewed/measured) pixel response times in the sub 6ms region, you're looking at £800+ in the 3440x1440p space. From the likes of Dell, LG, Acer.
Overdrive implementation is one of the most important factors in a gaming screen, and until the iiyama GB3461 is reviewed by someone like RTINGS (etc), I will continue to very much doubt it's on par with someone like LG Display.
Ultimately, you get what you pay for, with almost no exceptions.
So I stand by my comment - if you want a fast IPS, and you're moving from 27" 16:9 to UW 34", you need to dig a lot deeper in your pockets, unless you want to sacrifice spec.