Deep UV, visible blind, photoconductive devices fabricated on polycrystalline CVD diamond using inter-digitated planar electrodes have shown promising characteristics. The`as-fabricated' device performance is insufficient for many applications; a particularly demanding example is the monitoring of high power excimer lasers operating in the UV, which ideally require visible-blind, radiation hard fast UV detectors. However, post-growth treatments can strongly modify the performance level achieved. In this paper, we show that sequentially applied treatments can progressively change both the gain and speed of these devices. We have used charge sensitive deep level transient spectroscopy (Q-DLTS) to study the effect of these treatments on the defect structure of CVD material. For the first time, we report the realisation of diamond photoconductive devices capable of operating at more than 1 MHz at 193 nm.