From what I learned thus far with the Roadster.
V3 (tone stack triode) V5 (FX loop send) are cathode follower circuits. Either use Mesa (selected JJ tubes) or Chinese (have nickel plated clips on the plates). Russian made tubes will fail prematurely in the Cathode Follower circuits due to the voltage differential between the heater and cathode. An alternate is the JAN/GE 5751 which is supposed to be compliant with cathode follower circuits.
Somehow I believe that Mesa also selects their preamp tubes for matched triodes, otherwise there would be an out of balance signal to the power section (matched triodes are better served with Class A/B power amps, it probably does not matter much with the Simul Class circuits of the Mark Series amps but it does not hurt to used matched triode tubes there either).
I honestly prefer the Mesa tubes in the Roadster. I love the way the Mesa power tubes sound in this amp when saturated. They come close to the SED=C=6L6GC that I have used in the Mark V. I have experimented with EH EL34, TAD6L6GC STR, SED =C=, and KT77 (all of which I specifically ordered for my Mark V ) The TAD6L6GC-STR sounded great as well as the EH34's. I have not tried the newer set of SED =C= 6L6GC or the EL34 (in use with my RA100). I prefer the tone of the Ruby (Mesa Branded STR440 in the Roadster). Since I am not using the SED =C= 6L6GC at the moment (loaded the KT77 in the Mark V) I should give them a shot in the Roadster. I have also tried some of the different preamp tubes (EH, Tung Sol, Mullard reissue, Mullard CV4004, Preferred series 7025, and vintage Mesa Chinese tubes (which I think sound the best overall in my other amps). The Roadster seems to benefit tone wise with the Mesa branded JJ 12ax7a tubes. I did not notice much difference in gain structure, but I did notice more brightness with the Mullard reissue and a Sovtek LPS in V6. However, it became apparent that the tone I liked with the stock tubes was not the same with the different preamp tubes. My experience with the Mark V is quite the opposite, I did not like the Mesa JJ tubes, actually it is a fault with the power section as I believe it is running a much hotter bias than it should ( I have red plated many of the commonly bought tubes except for SED or Gold Lion KT77 ( I ordered them specifically for a fixed hot bias amp and so far no issues). Roadster and rest of the DR family, they run on the cold side as I recall.
The weak link is the rectifier tubes, not many available. I did try a NOS JAN 5U4G but it was a dud. I normally use either Mesa or EH 5U4G (same tube). I believe the Roadster would sound great with many of the 6L6GC tubes available since it has a moderate bias and does not run as hot as the Mark V.
If you were considering a different tube than a standard EL34, 6CA7 had some interesting character too them. (I would avoid the JJ 6CA7, many have had great success with the EH 6CA7). Also you can run the EL34B (lower bass response). As far as EL34 are concerned, the SED =C= EL34 are tops but much higher cost. Gold Lion KT77 are also a big expense. I like the EL34 (SED) the best.
The Svetlana (not true SED or Sevetlana from St Petersburg) are not too bad either (made by Reflektor, also makes Tung Sol, Sovtek, Mullard, etc...) I have been running them in my Mark IV for the past 2 years. Close but not close enough to the SED =C= tube. Tung Sol 7581 are also killer tubes (has more complex harmonics than the Svetlana). I have a quad of those, wonder what they would sound like in the Roadster ?