TBH I think it would be totally unfeasible to get a puppy - you could never house train it and it would be unfair (to put it mildly) on the pup to leave it alone for that length of time. Just under 6 hours is also, in my opinion and that of most of the rescue organisations I know, too long for an adult dog, especially on a regular basis. You would almost certainly end up with a trashed house and a dog or pup with behavioural problems.
For what it's worth, ResTroll, you do need to put the time in. For this reason, at echt Towers, we only got a puppy when I was on school holidays, to settle the beast in. I tell, you, I was knackered at the end of it, and happy to get back to work. And this is in Oz, where dogs are raised outside, and we can now put the puppy in his run in the yard when we go out to work. DC wanted a puppy, and I didn't, and she was gobsmacked at the amount of work involved in, as Brocspears puts it " growing it into the lovely family pet you have in mind".
Can you time this for when you are on holiday for a few weeks or more? To settle him, with crate training i don't really see a problem with it. We all have to leave our dogs for extended periods, but they cope - because they are dogs and whilst they are pack animals are used to spending periods of time alone in the wild! Certain breeds cope better than others. There are ways of avoiding separation anxiety and being there 24/7 for a puppy isn't one of them.
If you could get someone to look in on him and let him out for a tiddle at mid day then thats great too.
Alternate toys too as they get bored with the same toy and are stupid enough to think that the bone from last week is a brand spanking new one.
Managed properly i don't have a problem with dogs being left - take him for a nice walk before work should tire him out plenty to relax - after all, when you are home all day with your dog, what does it do? SLEEP
I'd call in at your vets and ask them which breed and age they would suggest based on your family and home and the time you can spend with it. Some breeds are better at being left alone than others which howl and chew things and generally try to follow you when you leave