FWIW--
I owned a CZ 527 American a few years ago. Equipped with the single set trigger. It was a BEAUTIFUL rifle; gorgeously figured walnut, and excellent blue and polish on the steel.
I own 3 Ruger M77 MkII Hawkeyes at present, and had a MkII Varmint/Target model years ago (220 Swift; stolen in Boise, ID, about 10 years ago...). 2 of my 3 Hawkeyes are the Predator model, which has the 2-stage trigger from the Target model. The 'regular' Hawkeye wears a Timney, but I have the LC6 parts. The walnut on my std Hawkeye isn't quite as beautiful as the CZ's was, but it's truly an amazing piece of wood to have come from Ruger.
Here's my comparison:
--COSMETICS. As I said above, the CZ was a beautiful rifle. The Rugers do not have the visual level of 'nice' that the CZ had, though my one Hawkeye is _surprisingly_ good.
--BOLT OPERATION (Ruger). The Rugers, as with all Rugers I've ever handled, have kind of 'clunky' bolts when new. They take time & working, or some lapping, to get them running fairly smoothly. They can still 'stick' sometimes if you're pushing the bolt handle in an odd direction, and they're kind of loose and floppy-feeling, but they're serviceable.
--BOLT OPERATION (CZ). The CZ's bolt action was too rough and sticky for me to fix by simply operating it at home (no ammunition in the same room) while watching TV. Neither did applying some abrasive or lapping compound fix it. That bolt would stick hard the majority of the time, even when I was trying to work the bolt slowly and carefully. Speed up and it'd stick hard every time. That CZ also pierced primers sometimes, with below-max-book loads. Chrono work verified that they were not 'hot' loads, too. I worked the nose of the firing pin a bit, but ultimately had to buy another assembly. CZ did not warranty it, although they were open and helpful when I called to talk about the issue and best way(s) to address it. The bluing on the tail end of the replacement firing pin assembly was matte and did not match the rifle at all.
--ACCURACY. The Rugers are all good to outstanding-shooting rifles. The Predators do indeed shoot better than I normally do. The Hawkeye gives good to great hunting accuracy (sub-MOA for 3 shots with loads it likes). They also don't copper up hardly at all. The CZ I could never get to shoot anywhere near what 'everyone' on the internet said their guns all shot. I discovered that there was interference between the stock, the magazine well metal, and the receiver that put it in a bind. It was TOUGH to re-assemble that rifle correctly. I relieved some of the wood and that helped, but it still wouldn't shoot the way the internet had led me to expect it should. Barrel clean-up was fast and easy.
--TRIGGERS. The CZ's trigger, when used conventionally, was not so great. Lots of gritty/jumpy creep, and not a clean break. The set trigger function was simply unsafe to have on a hunting rifle, IMO, although it was sure appealing at a target bench. The Rugers' 2-stage triggers (on the Predators and Target Model) are PHENOMENALLY GOOD. Crisp, clean, and beautiful. I prefer a 2-stage trigger anyway, but if you don't, the quality of the break may or may not make up for that for you. The Timney in the Hawkeye is great (I bought the gun with it already there), but too light for me to use in the cold on a hunting rifle with the supplied spring. Using Ruger's spring puts it on the light side of appropriate. I've put the std. LC6 parts back in just to try them, and at least on this gun that's nothing to write home about.
IME, you can almost run over a Ruger with a tractor, and still pick it up and use it. They're absolute tanks; super durable & reliable. The trigger mechanisms are very simple and open, like the pre-'64 Winchester 70's trigger was. This is an advantage in extraordinarily poor conditions. The CZ's SST is more complex and, IIRC, more enclosed.
Are the 550s different from the 527s? Do they run more smoothly? Did I get a 'bad one' from the factory? Don't know the answer to any of those questions from my own first-hand experience; never had nor fired any other CZs. I've looked at 550s over the years since having that 527, but could never get past the functional issues I'd had with it enough to try another.
I'd love to hear what you decide(d) to do.