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In my drawer, i have a compactflash-to-SATA adaptator and a 266x compact flash card. I forecast to build a speed SSD with this (for only 100€) to use for a system cache partition (where poser will be)

I would advise against it. Not only flash cards are slow to write to, they have a limited amount of write cycles per memory cell and have no wear-levelling, no write buffers, no read caches etc.

Then again if you're going for a real SSD, THAT I would say will get you get nice big boost - for a pricetag. My experiments with a OCZ 60Gb SSD housing Poser are showing a huge impact on loading times. But I also put caches to a 10000rpm disk since SSD writes don't give the same benefits for writing as they do for reading and also this way also the system doesn't have to read and write the same disk at the same time. While my WD Velociraptor is THE fastest HD I've yet to encounter (for home use, that is), it loses to my SSD in every possible measurement I've made (the most important being a real-time analysis of disk activity during actual Poser use).