ok, my naive attempts to circumvent any sw blits through the use of XRandr (for full-screen exclusivity) have failed miserably. as of now, i cannot get more than ~20fps even on framebuffers as small as 512^2, and shaders as simple as a couple of instructions.

for the record, under these conditions the benchmark shader outputs at 6.6fps at 512^2.

new XRandr'd version