Output tubes for ARC Ref 110

I am getting ready to replace the tubes in my ARC Ref 110.
I will be buying set of KT120 as main output tubes but was wondering if I should also replace at the same time the 6H30 stage tubes ?
I have done just a bit of reading and see that many people run the 6H30 much longer than the main power tubes.

What's the recommendation here ?

Life expectancy for 6H30 (normal conditions) is around 10,000 hours. 6550 around 2000. I'll assume the KT120 also 2000 hours.
Thanks !! 
Most people said the same thing as you but one person said to replace all 12 tubes in my amp.
I can confirm that the pre amp tube will have a much longer life up to 10,000 but not always 10,000hs than the output tubes usually given as 2,000 hrs. .  The 6H30s should be 6H30 EB for that rating you may only get 5,000 hrs out of standard 6H30s. so be careful;. 
HI Mechans

Do you mean I should get 6H30EB rather than 6H30 but that EB version would probably last half as long as standard 6H30 ?

No I mean the opposite.  From my reading, and I think you might want to research this on Audio Asylums Tube Asylum that the suffix tubes last a lot longer and are better over all than the standard meaning it is the 10,000 hr tube whereas the plain 6H30 would yield 5,000hrs. .  In particular there is yet another variant the 6H30 DR which is also highly prized.  It is not a tube I use or collect.

However almost every preamp or small signal tube last 2 to 4 times what the output tube it drives or effects.  I do use 6922s which are cousins of the 6H30s., or so I am told. I have yet to wear out a small signal tube. Even a pair I bought as worn out still work well. OTOH Worn outputs  really don't work.

One more question but regarding output tubes and bias.
My amp came with 6550 and the manual says to set the bias to about 65mA
Now that I have KT120 - do I still adjust to the same bias of 65mA or should it be adjusted to a different value ?

 Yes, bias them the same at 65ma. The KT 120s should last much longer than 6550s. I have heard around 4000 in the Ref 110.

OK....so just finished replacing the tubes and re-adjusting the bias.
The instructions say to adjust bias at the V5 tube to 65mVDC and then measure V7 to make sure it falls between 55 and 75 mVDC and do the same for other pairs.....

What I noticed is that  the mVDC at the main tube in the pair is showing as positive number (always 65mVDC) but when I check the voltage at the slave tube - I get negative reading...( ex: -60mVDC)
I was able to adjust the tubes and everything is as it should except for that reverse voltage for every slave in the pair.... I made sure I am not reversing the probes....
The manual doesn't say anything so I am just surprised.....