OP,
If you stated this already, I apologize. What kind of music do you listen to?
My feeling is that, unless you are a real head banger the PrimaLuna Evo300 should be adequate and you will experience a very significant improvement in sound quality. I use the word adequate because there are a lot of variables… I am feeling like I am getting pretty far out on a limb here. I have a PrimaLuna amp in my office. The pairing should sound very good. But, the power level is getting a bit low. From my listening to the ARC i-50 with the SF Nova Olympica was in a small room and they sounded fantastic and not at all constrained, but in a very large room it might be different.
However, I think ithe purchase would be very low risk. I think they would sound good / great and if PrimaLuna is either slightly underpowered or less refined, then you should be able to enjoy them until the time comes you can upgrade your electronics. In many ways this would be a classic upgrade cycle. Get a better speaker… save up and then upgrade electronics. So, from this perspective… sounds like a great move, gettin speakers you can grow into over time.