SME V tonearm versus Rega tonearms on Michell Orbe

Koetsu cartridges work phenomenally well with the SME 5 tonearm, but I have only tried the combo on two SOTA turntables and then on an SME 20 table, which I am presently using. There certainly was no extra bass on any of those, but I don't know the table you have in mind. I can't imagine using a Koetsu cartridge with a Rega arm--a no-compromise cartridge with a good bang for the buck arm sounds like a waste of cartrige dollars.

Believe it or not that's it's OK to compare these arms. I believe that analogue setup starts from CARTRIDGE first and ends with phono.
The downsides of Rega arms are tonarm and phono wires, somewhat suspension and counterweight. By modifying cheep Rega arms with Origin Live or Incognito, you will rich an increadible level of performance that is THE match to SME arms(just much less $$).
After Ingognito mods in my RB300 I've realized that I had to do it along with buying my GyroDec.

I think the limiting factor on the OL Rega arms has more to do with the relatively inconvenient, time consuming methods of setting the VTA, rather than the actual performance difference between it and the high-priced arms. If you get an OL RB 250 dialed in correctly to the cartridge I think it comes surprisingly close to the performance of high-priced arms (perhaps too close for the comfort of some expensive-arm owners). Hey, if I plunked down 2G's or more for a great arm, I wouldn't want to believe that a $500 arm could sound nearly as good either... :) But if and when I do move to a more expensive arm, it will be mainly because I want a faster way to set VTA.

You might want to explore the SME iV.vi if you are using an MC cartridge. The iV.vi was made to work with MC's and is suggested by Sumiko. If you get the VTA option and the breakout box, it is essentially the same price as the SME V. I frequently listen on an Orbe with the iV.vi and they are a very nice compliment to each other. Stepping down to the Rega makes little sense for the caliber of table and cartridge you are talking about.

I've just bought the Orbe SE + SME V + Benz M2 about 6 months ago. I had contemplated about the OL RB 250 as the option. For the price, the OL RB250 is hard to beat. Don't bother with the original RB250 arm, the OL mod is worth the additional few hundre bucks! However, the Michell tables were designed using the SME V arm. The SME V have more synergy with the Orbe than the Rega arms. I think the SME was SLIGHTLY bettered than the OL Rega in terms of fuller sound, wider soundstage, and more bass. (stress on slightly) But the OL RB250 comes very close to the SME V for a fraction of the price. It's that high-end thing, you pay $$$ for that extra 5-10% increase in performance. Is it worth the money? You will have to decide. I could not pay $3200 for an SME arm, so I had settled for an OL RB250. But while I was in Hong Kong earlier this year, I found the SME V from an authorized dealer was only selling for $1800. That was cheap enough for me to abandon the OL RB250 idea, and went for the SME V.

If you decide to get the OL RB250, it might be cheaper to get the arm directly from Origin Live from England. It would be cheaper than buying the arm here and sending it to OL in UK to get modified in most cases. Make sure you get the whole mod package. Like what others said earlier, adjusting VTA would be a pain in the butt on the RB arms. Good luck!