I've found my X60s to be very much like the old X31 I used to have, just improved in most all respects (speed, weight, heat, ...) It is just as silent as the X31 was, too. The only downside is that you have fewer docking options (you can only use an Ultrabase).
Now that the X61/s are out, I'm sure there are some good deals going around on the "old" X60 series.
I did have an X41 Tablet for a very short time; the clicking noise (helped a bit with the new HDD firmware, but still there) and general lack of performance/upgrade path of the 1.8" HDD was a bummer at best, and annoyed the heck out of me otherwise.
As an interim step, lowering the render quality of the Flash may help reduce performance issues -- as would an ad-blocking tool in your browser. You may find this fixes things so much, you don't even need to upgrade

(I use AdBlock Plus with Firefox, works well out of the box.)