I'm running Poser 7(!) on an external SSD (obviously not my primary drive). It works great.  Loads of up fast, but seems to work about the same as before. Had it on my primary (C) SSD drive, but that got crowded because of so many other programs so I put it on an external SSD. No problems whatsoever. Still running Poser 7 because I'm focusing more on stuff like After Effects, Photoshop, Illustrator, using Poser mostly as an accessory now.

True, SSDs have been more expensive even at smaller capacity, but the size/price ratio is getting better. The 80 GB external I got was about half what I paid for the internal 80 GB 2 years ago. Of course, quality is an issue, so careful shopping is a definite prerequisite to buying one.