The performance would be reasonable. The bottleneck with Pocket Quake is that it still contains floating point math within the 3D part of the engine. The rasterization code, which is the only part of the engine that has to work harder to render at a higher resolution, is all integer math. That is why PQ running at 320x240 (landscape) is only around 20% slower than 240x160 (portrait) even though it is rendering twice as many pixels.
So 640x480 is certainly feasible. I estimate somewhere around 10 FPS at that resolution on an a730, not overclocked.
If I had such a device I would modify PQ to support that resolution.
Dan East