Should I upgrade my Linn Axis to a Rega RP40?

I hope you are aware of the price that this special 40th anniversary table. If you have the means, then you might want to audition the table. If you can work with a dealer that should to give you the an accurate impression of the table's sound.

I just picked up the RP40 yesterday, and am listening to it as I write this. Since I've never heard an Axis, I can't offer you a comparison there, but I can vouch for the RP40 vs. the RP3. Although I don't own an RP3 myself, I have heard it enough to assure you that the RP40 is a significant step up, and definitely worth the money.

Before the RP40 was announced, I had been considering the RP6 (the model up from the RP3, US$400 more than the RP40 and US$900 more than the RP3) so while I was at the store yesterday, I took the opportunity to compare the two using my own vinyl. The comparison almost convinced me to switch back to the RP6, but I decided to stick with the 40th Anniversary model instead for three reasons:

First of all, when it comes time to replace the stylus, an upgrade will reduce the performance gap between the two turntables significantly. There are other upgrade options as well. For example, the RP6 platter will fit on the RP40 with the aluminium platter adapter.

Second, I don't judge the rest of my system to be good enough yet to justify the purchase of an RP6. I'd rather put the $400 I saved toward a desperately needed speaker upgrade, which will have a much greater impact on my listening enjoyment than an RP6.

Finally, owning the Rega 40th anniversary model is just really, really cool!

As Mechans points out, you really need to hear it to decide. If you don't have access to a Rega dealer then, well, you have my sympathies. Based on the mini autobiography you included in your post, and the sweet sounds I've heard from my RP40 so far, I'm pretty sure you would be very happy it.