both are pretty much the same..
merlin has, in theory better brakes, but white triban 5 for e.g. has the same as my triban 3 and they have lasted for ages and still work fine.
wheelsets on both are ??? as they are unknown brand etc but should last 2-3k miles no problems.. I eat wheels for lunch and I killed mine in 1.4k miles
I'd probably go with that green felt in 58cm.. awesome looking bike(seen a few around london) and from my previous experience felt make good in house parts so hubs etc should last for ages.
edit -;
no I own-ish a triban 3
but it has been rebuilt a few times due to me hating the way it looked, if 3 is anything to go by 5 will be great and I've only heard good things about 5.. and now 5(white) is on offer at £399 - possibly best bang for buck..
out of the 3 -;
felt
merlin
b'twin
you can't go wrong with either one of them to be honest.