Re: CZ 452 Varment or Ruger M77-22?
Thats a great choice! like Jr. V said though, they are very hard to find. if you end up wanting something sooner, I'd go with the CZ or the Savage Mark II. i think you would have to invest more money into the 77/22 to get it to the point of the other two out of the box (if you get a $15 trigger kit for the CZ and self install). i have a CZ 452 and am very pleased with it.
looking at it from a training point of view, maybe the 452 is your best bet as the trigger is more similar in feel to your 5R than the accutrigger, though both are great. as you seem to have come to yourself, i would try to match your 22 trainer to your 5R as much as possible, i.e. scope features, stock feel, trigger pull, etc.