Depends what price the new models are. So far Apple has kept US pricing constant but bumped up overseas pricing on new models (e.g. price of iPhone 14 Pro = iPhone 13 Pro on launch in US, but iPhone 14 Pro > iPhone 13 Pro on launch in Europe).
Is 4th gen the one with the A12X? If so, I think getting the 5th gen/M1 version is a sensible minimum for now as the M1 looks like it is going to be a big cut-off point for features and support in the future.