I got a 44-700 to replace a failing 44-500. The differences in the -700 model is the front blue led's seem a little brighter and now we get phantom caller ID notices when on the phone, or past caller ID notices from calls that occurred earlier in the day. Never had that problem on the -500 model.
Tech said they rarely get HR34s anymore, but when they do they have to use it. Sometimes they get one pallet in and he hates putting them in. He said a lot of the times those HR34 installs end up becoming repeat calls because the users get frustrated how slow the unit is. He doesn't like to have repeat calls under his belt so he prefers the 44's. He said the 54's are only ever used on 4K installs, which so far hasn't been very popular in our county.