Sorry, must have missed you first time around.
Your 10m time is always going to be around 18-20 secs per mile slower than your 5m time (assuming similar terrain). Maybe a bit closer if you are really a long-distance dude. So, based on your 29.07/8km (5.51m/m), you should expect to be able to run (always approx) 61.50 for 10m. So, you are not a million miles away with 63.12.
Your long run pace of 7.30-7.40 seems in the right place (could maybe be a bit slower), but you give no further information about the rest of the week. Also, you give no indication of what 7.30 pace "costs" you. (Like saying that your HRmax is 177, and your long run of 7.30m/m is done at 130 HR. Such information would let me know more how to help).
It's possible that your long runs (and the other runs of the week) are not as "easy" as they should be.
Endurance comes from the legs, not from working at medium-high HR's. So you must always be careful to go slow enough (and long enough) that they are able to adapt properly. Pushing the pace in 5-milers and 6-milers, while fun, will not do much for your long term endurance ability.
5k+60 is actually quite a tough pace, and I am not surprised that you found a straight 10 miles at that pace to be a hard workout. This is yet more evidence that you are right when you say your endurance is not as it should be.
Tell me a little bit more about the rest of your week (including paces) and I will see if I can offer some advice.