RE: World Models Ultimate 40
As far as flying goes - it's a Great model to fly, quite aerobatic yet stable - a good 1st Bipe. If you can handle the other two planes you mention, you can handle one of these.
Ours flew very happily with an OS 40FX, 10x6 Prop, 10% Nitro fuel.
They build really easily, the instructions are clear and correct and it's supplied with the necessary jigs to get the wing alignment right. Ours was built straight out of the box and we used all of the standard hardware. Everything fitted correctly.
A couple of points
We found that the gluing was lacking in some areas, If I was to buy another one, I would certainly add CA to as many joints as I could access before I did anything else to it. I would even use some thin tubing off the CA bottle to access the joints that I couldn't otherwise reach
Also look at the front firewall to see if you can add some triangular gusset to tie it back to the fuselage a bit stronger - ours came loose on its first flight so it was removed, triangular gusset added to assist in tying it back to the fuselage and it was epoxied back in place.
Having said those two things, I know that many others haven't had any problems with theirs so ours may have one of the unlucky ones.